diff --git a/INSTALL.md b/INSTALL.md
index c703b72af3..60541d61f5 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -424,6 +424,15 @@ functions replacing the dgemm calls with `offload_dgemm` will eventually be offl
 The SPLA library has internal criteria to decide if it is worth to do the operation on GPU or not.
 Calls to `offload_dgemm` also accept pointers on GPU or a combination of them.
 
+### 2y. libgrpp (optional, enables calculations with ECPs)
+
+- libgrpp is a library for the calculation of integrals with GTOs and ECPs
+- The libgrpp library can be found under <https://github.com/aoleynichenko/libgrpp>
+- During the installation, the directories `$(LIBGRPP_DIR)/lib` and `$(LIBGRPP_DIR)/include` are
+  created.
+- Add `-D__LIBGRPP` to DFLAGS, `-I$(LIBGRPP_DIR)/include` to FCFLAGS and
+  `-L$(LIBGRPP_DIR)/lib -llibgrpp` to LIBS
+
 <!---
 ### 2y. LibMaxwell (External Maxwell Solver)
 
@@ -508,6 +517,7 @@ libraries (see 2.)
 - `-D__parallel -D__SCALAPACK` parallel runs
 - `-D__LIBINT` use LIBINT (needed for HF exchange)
 - `-D__LIBXC` use LIBXC
+- `-D__LIBGRPP` use libgrpp (for calculations with ECPs)
 - `-D__ELPA` use ELPA in place of SYEVD to solve the eigenvalue problem
 - `-D__FFTW3` FFTW version 3 is recommended
 - `-D__MKL` link the MKL library for linear algebra and/or FFT
diff --git a/data/ECP_POTENTIALS_pob-TZVP-rev2 b/data/ECP_POTENTIALS_pob-TZVP-rev2
index ae1c23ed0e..a156aae4f6 100644
--- a/data/ECP_POTENTIALS_pob-TZVP-rev2
+++ b/data/ECP_POTENTIALS_pob-TZVP-rev2
@@ -10,663 +10,760 @@
 pob-TZVP-rev2
 Rb nelec 28
 Rb ul
-2  1.000000    0.000000
+2      1.00000000             0.00000000
 Rb S
-0  5.031683377 89.503949586
-0  2.015185434 0.437903605
+2      5.03168338            89.50394959
+2      2.01518543             0.43790360
 Rb P
-0  4.383544458 19.520470196
-0  4.332659280 39.038955357
-0  1.374288087 0.170609341
-0  1.225772391 0.418499875
+2      4.38354446            19.52047020
+2      4.33265928            39.03895536
+2      1.37428809             0.17060934
+2      1.22577239             0.41849988
 Rb D
-0  3.415601371 10.482661239
-0  3.412863366 15.724060278
-0  1.030504898 0.266082838
-0  1.019872163 0.408802184
+2      3.41560137            10.48266124
+2      3.41286337            15.72406028
+2      1.03050490             0.26608284
+2      1.01987216             0.40880218
 Rb F
-0  3.574403408 -4.478284427
-0  3.565710590 -5.956907509
+2      3.57440341            -4.47828443
+2      3.56571059            -5.95690751
 Sr nelec 28
 Sr ul
-2  1.000000    0.000000
+2      1.00000000             0.00000000
 Sr S
-0  6.933460990 135.271042909
-0  4.114003832 17.944071402
+2      6.93346099           135.27104291
+2      4.11400383            17.94407140
 Sr P
-0  7.216816623 29.438081345
-0  7.173696172 58.880674863
-0  3.022798817 4.936282692
-0  2.865699030 9.723352071
+2      7.21681662            29.43808135
+2      7.17369617            58.88067486
+2      3.02279882             4.93628269
+2      2.86569903             9.72335207
 Sr D
-0  6.321514600 11.907239187
-0  6.391499495 17.859551440
-0  1.769726597 2.199180226
-0  1.636771665 2.893570866
+2      6.32151460            11.90723919
+2      6.39149949            17.85955144
+2      1.76972660             2.19918023
+2      1.63677166             2.89357087
 Sr F
-0  4.244198396 -5.509333254
-0  4.229164471 -7.304641693
+2      4.24419840            -5.50933325
+2      4.22916447            -7.30464169
 Y nelec 28
 Y ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Y S
-0     7.858275  135.134974
-0     3.382128   15.411632
+2      7.85827500           135.13497400
+2      3.38212800            15.41163200
 Y P
-0     6.849791   29.251437
-0     6.710092   58.508363
-0     3.042159    3.780243
-0     2.937330    7.676547
+2      6.84979100            29.25143700
+2      6.71009200            58.50836300
+2      3.04215900             3.78024300
+2      2.93733000             7.67654700
 Y D
-0     5.416315   11.849911
-0     5.333416   17.778103
-0     1.976212    2.062383
-0     1.961111    3.075654
+2      5.41631500            11.84991100
+2      5.33341600            17.77810300
+2      1.97621200             2.06238300
+2      1.96111100             3.07565400
 Y F
-0     5.028590   -6.928078
-0     5.005582   -9.155099
+2      5.02859000            -6.92807800
+2      5.00558200            -9.15509900
 Zr nelec 28
 Zr ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Zr S
-0     8.636528  150.242994
-0     3.717639   18.780036
+2      8.63652800           150.24299400
+2      3.71763900            18.78003600
 Zr P
-0     7.626728   33.192791
-0     7.453207   66.389039
-0     3.358389    4.620726
-0     3.229738    9.260270
+2      7.62672800            33.19279100
+2      7.45320700            66.38903900
+2      3.35838900             4.62072600
+2      3.22973800             9.26027000
 Zr D
-0     5.938086   13.993383
-0     5.825544   20.995882
-0     2.205019    2.285166
-0     2.206292    3.441260
+2      5.93808600            13.99338300
+2      5.82554400            20.99588200
+2      2.20501900             2.28516600
+2      2.20629200             3.44126000
 Zr F
-0     4.800215   -5.239320
-0     4.798992   -6.987424
+2      4.80021500            -5.23932000
+2      4.79899200            -6.98742400
 Nb nelec 28
 Nb ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Nb S
-0     9.376578  165.156736
-0     4.043572   21.823951
+2      9.37657800           165.15673600
+2      4.04357200            21.82395100
 Nb P
-0     8.363609   37.249284
-0     8.166898   74.507389
-0     3.693075    5.439486
-0     3.551047   10.913252
+2      8.36360900            37.24928400
+2      8.16689800            74.50738900
+2      3.69307500             5.43948600
+2      3.55104700            10.91325200
 Nb D
-0     6.689108   15.214549
-0     6.537193   22.833508
-0     2.551118    3.000052
-0     2.567896    4.553734
+2      6.68910800            15.21454900
+2      6.53719300            22.83350800
+2      2.55111800             3.00005200
+2      2.56789600             4.55373400
 Nb F
-0     5.568285   -6.281354
-0     5.671372   -8.755644
+2      5.56828500            -6.28135400
+2      5.67137200            -8.75564400
 Mo nelec 28
 Mo ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Mo S
-0    10.097000  180.076853
-0     4.375670   24.715920
+2     10.09700000           180.07685300
+2      4.37567000            24.71592000
 Mo P
-0     9.126564   41.227678
-0     8.863223   82.452670
-0     4.044948    6.345092
-0     3.866657   12.458423
+2      9.12656400            41.22767800
+2      8.86322300            82.45267000
+2      4.04494800             6.34509200
+2      3.86665700            12.45842300
 Mo D
-0     7.535754   19.308744
-0     7.278976   28.977674
-0     2.763205    3.189516
-0     2.772085    4.700169
+2      7.53575400            19.30874400
+2      7.27897600            28.97767400
+2      2.76320500             3.18951600
+2      2.77208500             4.70016900
 Mo F
-0     6.306633   -7.178888
-0     6.356448   -9.745978
+2      6.30663300            -7.17888800
+2      6.35644800            -9.74597800
+Tc nelec 28
+Tc ul
+2      1.00000000             0.00000000
+Tc S
+2     10.79936900           195.09130300
+2      4.70725700            27.34041300
+Tc P
+2      9.82669900            45.06081200
+2      9.56111500            90.11729500
+2      4.37857800             7.07051700
+2      4.19090700            14.04801900
+Tc D
+2      8.33604500            21.65775500
+2      8.24453300            32.47195900
+2      3.09370700             3.78952500
+2      3.16872200             6.05343000
+Tc F
+2      7.04094000            -7.99562300
+2      7.06947300           -10.74569600
 Ru nelec 28
 Ru ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Ru S
-0    11.500590  209.786493
-0     5.068575   30.214307
+2     11.50059000           209.78649300
+2      5.06857500            30.21430700
 Ru P
-0    10.532634   48.751244
-0    10.192010   97.496529
-0     4.734892    7.860188
-0     4.509065   15.329751
+2     10.53263400            48.75124400
+2     10.19201000            97.49652900
+2      4.73489200             7.86018800
+2      4.50906500            15.32975100
 Ru D
-0     8.877977   26.967506
-0     8.766122   40.432303
-0     3.170196    3.340758
-0     3.228851    5.256352
+2      8.87797700            26.96750600
+2      8.76612200            40.43230300
+2      3.17019600             3.34075800
+2      3.22885100             5.25635200
 Ru F
-0     7.820249   -8.847525
-0     7.839647  -11.835518
+2      7.82024900            -8.84752500
+2      7.83964700           -11.83551800
 Rh nelec 28
 Rh ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Rh S
-0    12.194816  225.312054
-0     5.405137   32.441582
+2     12.19481600           225.31205400
+2      5.40513700            32.44158200
 Rh P
-0    11.280755   52.872826
-0    10.927248  105.745526
-0     5.090117    8.619344
-0     4.851832   16.973459
+2     11.28075500            52.87282600
+2     10.92724800           105.74552600
+2      5.09011700             8.61934400
+2      4.85183200            16.97345900
 Rh D
-0     9.136337   25.108501
-0     8.964808   37.695731
-0     3.643612    4.202584
-0     3.636007    6.292790
+2      9.13633700            25.10850100
+2      8.96480800            37.69573100
+2      3.64361200             4.20258400
+2      3.63600700             6.29279000
 Rh F
-0     8.616228   -9.673568
-0     8.629435  -12.899847
+2      8.61622800            -9.67356800
+2      8.62943500           -12.89984700
 Pd nelec 28
 Pd ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Pd S
-0    12.798825  240.262789
-0     5.800528   34.729961
+2     12.79882500           240.26278900
+2      5.80052800            34.72996100
 Pd P
-0    11.874697   56.746929
-0    11.474335  113.444417
-0     5.515999    9.345639
-0     5.248043   18.345447
+2     11.87469700            56.74692900
+2     11.47433500           113.44441700
+2      5.51599900             9.34563900
+2      5.24804300            18.34544700
 Pd D
-0     8.502212   28.595554
-0     7.983324   43.453921
-0     3.107628    1.852286
-0     2.476734    1.406765
+2      8.50221200            28.59555400
+2      7.98332400            43.45392100
+2      3.10762800             1.85228600
+2      2.47673400             1.40676500
 Pd F
-0     9.679571  -10.987255
-0     9.691349  -14.626190
+2      9.67957100           -10.98725500
+2      9.69134900           -14.62619000
 Ag nelec 28
 Ag ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Ag S
-0    12.567714  255.054771
-0     6.997662   36.983393
+2     12.56771400           255.05477100
+2      6.99766200            36.98339300
 Ag P
-0    11.316496   60.715705
-0    10.958063  121.443889
-0     7.111400   10.171866
-0     6.773319   20.486564
+2     11.31649600            60.71570500
+2     10.95806300           121.44388900
+2      7.11140000            10.17186600
+2      6.77331900            20.48656400
 Ag D
-0     8.928437   29.504938
-0    11.102567   44.018736
-0     5.543212    5.368333
-0     3.928835    7.408375
+2      8.92843700            29.50493800
+2     11.10256700            44.01873600
+2      5.54321200             5.36833300
+2      3.92883500             7.40837500
 Ag F
-0    11.012913  -12.623403
-0    11.019898  -16.764327
+2     11.01291300           -12.62340300
+2     11.01989800           -16.76432700
 Cd nelec 28
 Cd ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Cd S
-0    13.355176  270.039448
-0     7.308378   38.877766
+2     13.35517600           270.03944800
+2      7.30837800            38.87776600
 Cd P
-0    12.659728   64.607470
-0    12.289639  129.219445
-0     6.786176   10.622558
-0     6.400743   21.265046
+2     12.65972800            64.60747000
+2     12.28963900           129.21944500
+2      6.78617600            10.62255800
+2      6.40074300            21.26504600
 Cd D
-0    11.161722   31.663965
-0    11.219615   47.489216
-0     4.537733    5.186200
-0     4.335727    7.566063
+2     11.16172200            31.66396500
+2     11.21961500            47.48921600
+2      4.53773300             5.18620000
+2      4.33572700             7.56606300
 Cd F
-0    11.478986  -12.632785
-0    11.487027  -16.760171
+2     11.47898600           -12.63278500
+2     11.48702700           -16.76017100
 In nelec 28
 In ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 In S
-0    15.392822  281.122350
-0     8.055864   61.901470
+2     15.39282200           281.12235000
+2      8.05586400            61.90147000
 In P
-0    13.928672   67.462154
-0    13.347234  134.949250
-0     7.614132   14.746140
-0     7.318365   29.639262
+2     13.92867200            67.46215400
+2     13.34723400           134.94925000
+2      7.61413200            14.74614000
+2      7.31836500            29.63926200
 In D
-0    14.034715   35.493254
-0    14.511616   53.178773
-0     5.550550    9.177281
-0     5.059415   12.392410
+2     14.03471500            35.49325400
+2     14.51161600            53.17877300
+2      5.55055000             9.17728100
+2      5.05941500            12.39241000
 In F
-0    12.539056  -13.728078
-0    12.552561  -18.206866
+2     12.53905600           -13.72807800
+2     12.55256100           -18.20686600
 Sn nelec 28
 Sn ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Sn S
-0    17.420414  279.988682
-0     7.631155   62.377810
+2     17.42041400           279.98868200
+2      7.63115500            62.37781000
 Sn P
-0    16.131024   66.162523
-0    15.628077  132.174396
-0     7.325608   16.339417
-0     6.942519   32.488959
+2     16.13102400            66.16252300
+2     15.62807700           132.17439600
+2      7.32560800            16.33941700
+2      6.94251900            32.48895900
 Sn D
-0    15.514976   36.387441
-0    15.188160   54.507841
-0     5.456024    8.696823
-0     5.363105   12.840208
+2     15.51497600            36.38744100
+2     15.18816000            54.50784100
+2      5.45602400             8.69682300
+2      5.36310500            12.84020800
 Sn F
-0    12.282348  -12.576333
-0    12.272150  -16.595944
+2     12.28234800           -12.57633300
+2     12.27215000           -16.59594400
 Sb nelec 28
 Sb ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Sb S
-0    16.330865  281.071581
-0     8.556542   61.716604
+2     16.33086500           281.07158100
+2      8.55654200            61.71660400
 Sb P
-0    14.470337   67.457380
-0    13.816194  134.933503
-0     8.424924   14.716344
-0     8.092728   29.518512
+2     14.47033700            67.45738000
+2     13.81619400           134.93350300
+2      8.42492400            14.71634400
+2      8.09272800            29.51851200
 Sb D
-0    14.886331   35.447815
-0    15.146319   53.143466
-0     5.908267    9.179223
-0     5.594322   13.240253
+2     14.88633100            35.44781500
+2     15.14631900            53.14346600
+2      5.90826700             9.17922300
+2      5.59432200            13.24025300
 Sb F
-0    14.444978  -15.366801
-0    14.449295  -20.296138
+2     14.44497800           -15.36680100
+2     14.44929500           -20.29613800
 Te nelec 28
 Te ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Te S
-0    16.814473  281.045843
-0     8.793526   61.620656
+2     16.81447300           281.04584300
+2      8.79352600            61.62065600
 Te P
-0    14.877801   67.449464
-0    14.269731  134.904304
-0     8.724435   14.689547
-0     8.291515   29.415063
+2     14.87780100            67.44946400
+2     14.26973100           134.90430400
+2      8.72443500            14.68954700
+2      8.29151500            29.41506300
 Te D
-0    15.205008   35.432057
-0    15.225848   53.135687
-0     6.071769    9.069802
-0     5.804760   13.122304
+2     15.20500800            35.43205700
+2     15.22584800            53.13568700
+2      6.07176900             9.06980200
+2      5.80476000            13.12230400
 Te F
-0    15.206168  -15.745450
-0    15.201702  -20.742448
+2     15.20616800           -15.74545000
+2     15.20170200           -20.74244800
 I nelec 28
 I ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 I S
-0    40.033376   49.989649
-0    17.300576  281.006556
-0     8.851720   61.416739
+2     40.03337600            49.98964900
+2     17.30057600           281.00655600
+2      8.85172000            61.41673900
 I P
-0    15.720141   67.416239
-0    15.208222  134.807696
-0     8.294186   14.566548
-0     7.753949   28.968422
+2     15.72014100            67.41623900
+2     15.20822200           134.80769600
+2      8.29418600            14.56654800
+2      7.75394900            28.96842200
 I D
-0    13.817751   35.538756
-0    13.587805   53.339759
-0     6.947630    9.716466
-0     6.960099   14.977500
+2     13.81775100            35.53875600
+2     13.58780500            53.33975900
+2      6.94763000             9.71646600
+2      6.96009900            14.97750000
 I F
-0    18.522950  -20.176618
-0    18.251035  -26.088077
-0     7.557901   -0.220434
-0     7.597404   -0.221646
+2     18.52295000           -20.17661800
+2     18.25103500           -26.08807700
+2      7.55790100            -0.22043400
+2      7.59740400            -0.22164600
+Xe nelec 28
+Xe ul
+2      1.00000000             0.00000000
+Xe S
+2     40.00518400            49.99796200
+2     17.81221400           281.01330300
+2      9.30415000            61.53825500
+Xe P
+2     15.70177200            67.43914200
+2     15.25860800           134.87471100
+2      9.29218400            14.66330000
+2      8.55900300            29.35473000
+Xe D
+2     15.18560000            35.43690800
+2     14.28450000            53.19577200
+2      7.12188900             9.04623200
+2      6.99196300            13.22368100
+2      0.62394600             0.08485300
+2      0.64728400             0.04415500
+Xe F
+2     20.88155700           -23.08929500
+2     20.78344300           -30.07447500
+2      5.25338900            -0.28822700
+2      5.36118800            -0.38692400
 Cs nelec 46
 Cs ul
-2  1.000000    0.000000
+2      1.00000000             0.00000000
 Cs S
-0  4.081119213 84.547722330
-0  2.421522383 16.654034970
+2      4.08111921            84.54772233
+2      2.42152238            16.65403497
 Cs P
-0  5.533972644 52.349630743
-0  5.506794384 104.699413178
-0  2.280961580 8.806557725
-0  2.103490505 17.616611106
+2      5.53397264            52.34963074
+2      5.50679438           104.69941318
+2      2.28096158             8.80655772
+2      2.10349050            17.61661111
 Cs D
-0  1.813149410 5.268985513
-0  1.807721684 7.903641922
-0  0.872904031 1.336431281
-0  0.858720279 2.005651328
+2      1.81314941             5.26898551
+2      1.80772168             7.90364192
+2      0.87290403             1.33643128
+2      0.85872028             2.00565133
 Cs F
-0  5.217083860 -16.497654298
-0  5.148196479 -23.308131339
-0  1.580599469 -2.236827346
-0  1.347895923 -2.226941952
+2      5.21708386           -16.49765430
+2      5.14819648           -23.30813134
+2      1.58059947            -2.23682735
+2      1.34789592            -2.22694195
 Cs G
-0  1.807739822 -2.504198722
-0  1.805061309 -3.138244524
+2      1.80773982            -2.50419872
+2      1.80506131            -3.13824452
 Ba nelec 46
 Ba ul
-2  1.000000    0.000000
+2      1.00000000             0.00000000
 Ba S
-0  4.177931587 84.785457583
-0  2.522632800 17.372709041
+2      4.17793159            84.78545758
+2      2.52263280            17.37270904
 Ba P
-0  6.294119351 52.512225743
-0  6.476457746 105.022668647
-0  2.284326647 8.707014937
-0  2.091555201 17.165458832
+2      6.29411935            52.51222574
+2      6.47645775           105.02266865
+2      2.28432665             8.70701494
+2      2.09155520            17.16545883
 Ba D
-0  1.925291745 5.346535679
-0  1.878534118 8.025720742
-0  0.907088727 1.346295081
-0  0.910060953 2.063710453
+2      1.92529174             5.34653568
+2      1.87853412             8.02572074
+2      0.90708873             1.34629508
+2      0.91006095             2.06371045
 Ba F
-0  6.256321669 -20.003223472
-0  6.134135837 -26.118214748
-0  1.641382784 -2.344457989
-0  1.599343316 -2.980867480
+2      6.25632167           -20.00322347
+2      6.13413584           -26.11821475
+2      1.64138278            -2.34445799
+2      1.59934332            -2.98086748
 Ba G
-0  2.142381001 -3.316602759
-0  2.159981109 -4.275647018
+2      2.14238100            -3.31660276
+2      2.15998111            -4.27564702
 Hf nelec 60
 Hf ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Hf S
-0    10.248856  478.237404
-2    10.729127    0.388024
-0     1.964856   -1.071232
+2     10.24885550           478.23740400
+4     10.72912730             0.38802390
+2      1.96485640            -1.07123160
 Hf P
-0     8.683462  101.046818
-0     7.916920  212.197761
-2     9.379243    0.132646
-2     8.244209    0.453108
-0     1.596686   -0.407914
-0     1.710281   -0.561817
+2      8.68346220           101.04681830
+4      9.37924270             0.13264580
+2      1.59668640            -0.40791377
+2      7.91692000           212.19776093
+4      8.24420880             0.45310787
+2      1.71028050            -0.56181693
 Hf D
-0     5.189557   43.115467
-0     5.253229   65.934732
-2     5.937871    0.025912
-2     5.712906    0.033741
-0     1.014856   -0.280579
-0     0.473712   -0.084849
+2      5.18955690            43.11546688
+4      5.93787150             0.02591168
+2      1.01485580            -0.28057888
+2      5.25322860            65.93473230
+4      5.71290630             0.03374112
+2      0.47371160            -0.08484924
 Hf F
-0     1.912608    4.811801
-0     1.880740    6.418574
+2      1.91260790             4.81180110
+2      1.88074000             6.41857354
 Hf G
-0     2.724180   -4.636585
-0     2.708953   -5.767288
+2      2.72418010            -4.63658493
+2      2.70895290            -5.76728839
 Ta nelec 60
 Ta ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Ta S
-0    10.318069  454.600649
-2    10.540267    2.837975
-0     2.574726   -0.814736
+2     10.31806920           454.60064950
+4     10.54026710             2.83797470
+2      2.57472570            -0.81473570
 Ta P
-0     8.743342   96.910783
-0     7.916223  195.850432
-2     9.275736    4.812524
-2     8.101675    6.338512
-0     2.077127   -0.459173
-0     2.750372   -0.644586
+2      8.74334250            96.91078317
+4      9.27573600             4.81252367
+2      2.07712710            -0.45917270
+2      7.91622270           195.85043193
+4      8.10167530             6.33851240
+2      2.75037230            -0.64458633
 Ta D
-0     5.447314   45.969976
-0     5.212545   69.638972
-2     5.884358    0.802933
-2     5.649579    0.429595
-0     1.388180   -0.307227
-0     1.294398   -0.461560
+2      5.44731350            45.96997556
+4      5.88435790             0.80293292
+2      1.38818040            -0.30722744
+2      5.21254550            69.63897162
+4      5.64957850             0.42959538
+2      1.29439830            -0.46155978
 Ta F
-0     2.161275    5.757773
-0     2.125939    7.678167
+2      2.16127540             5.75777263
+2      2.12593940             7.67816674
 Ta G
-0     3.145920   -5.684066
-0     3.127942   -7.062313
+2      3.14592010            -5.68406551
+2      3.12794180            -7.06231256
 W nelec 60
 W ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 W S
-0    11.063795  419.227599
-0     8.217641   41.191307
+2     11.06379490           419.22759860
+2      8.21764150            41.19130670
 W P
-0     9.338188  107.348110
-0     8.430448  214.699568
-2     9.490020    0.025442
-2     9.489947    0.051895
-0     1.882997   -0.117184
-0     1.906972    0.296689
+2      9.33818790           107.34811040
+4      9.49002000             0.02544197
+2      1.88299720            -0.11718450
+2      8.43044810           214.69956847
+4      9.48994740             0.05189533
+2      1.90697160             0.29668853
 W D
-0     6.205433   58.881279
-0     6.122157   98.683556
-2     6.274556    0.019537
-2     6.226375    0.021956
-0     1.963875   -0.088577
-0     1.888287   -0.209726
+2      6.20543310            58.88127856
+4      6.27455610             0.01953668
+2      1.96387520            -0.08857656
+2      6.12215660            98.68355616
+4      6.22637500             0.02195628
+2      1.88828660            -0.20972592
 W F
-0     2.307953    6.232472
-0     2.270609    8.311345
+2      2.30795340             6.23247244
+2      2.27060870             8.31134457
 W G
-0     3.583491   -6.802944
-0     3.562515   -8.443232
+2      3.58349080            -6.80294404
+2      3.56251490            -8.44323222
 Re nelec 60
 Re ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Re S
-0    12.163814  421.970300
-0     7.107595   50.134439
+2     12.16381440           421.97029970
+2      7.10759460            50.13443870
 Re P
-0     9.684597   88.481910
-0     9.476214  176.787220
-0     7.668066   10.434338
-0     5.055156   20.458743
+2      9.68459710            88.48190993
+2      9.47621410           176.78721967
+2      7.66806580            10.43433833
+2      5.05515620            20.45874300
 Re D
-0     6.509888   43.162431
-0     6.091216   64.767759
-0     4.164006    5.340301
-0     4.407379    8.243332
+2      6.50988840            43.16243064
+2      6.09121580            64.76775930
+2      4.16400600             5.34030112
+2      4.40737860             8.24333232
 Re F
-0     2.562658    7.244543
-0     2.521549    9.659266
+2      2.56265840             7.24454254
+2      2.52154870             9.65926634
 Re G
-0     4.034599   -7.974940
-0     4.009628   -9.882736
+2      4.03459850            -7.97494049
+2      4.00962760            -9.88273633
 Os nelec 60
 Os ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Os S
-0    13.002001  424.390376
-0     6.962763   57.122503
+2     13.00200150           424.39037620
+2      6.96276350            57.12250300
 Os P
-0    10.498941   88.279003
-0     9.992523  176.486064
-0     6.588248   11.715012
-0     5.037167   22.915006
+2     10.49894090            88.27900273
+2      9.99252300           176.48606367
+2      6.58824770            11.71501200
+2      5.03716750            22.91500633
 Os D
-0     7.083441   44.777708
-0     6.721179   67.153648
-0     3.794626    5.550387
-0     3.748125    8.220104
+2      7.08344080            44.77770836
+2      6.72117940            67.15364760
+2      3.79462620             5.55038728
+2      3.74812500             8.22010362
 Os F
-0     2.826276    8.328332
-0     2.781198   11.103102
+2      2.82627570             8.32833249
+2      2.78119820            11.10310240
 Os G
-0     4.496981   -9.181343
-0     4.467738  -11.361604
+2      4.49698090            -9.18134298
+2      4.46773820           -11.36160383
 Ir nelec 60
 Ir ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Ir S
-0    13.831474  426.958149
-0     7.047914   65.338813
+2     13.83147390           426.95814900
+2      7.04791390            65.33881260
 Ir P
-0    11.106433   88.075442
-0    10.456552  176.124770
-0     6.379614   12.682260
-0     5.064726   24.635949
+2     11.10643310            88.07544227
+2     10.45655210           176.12477027
+2      6.37961400            12.68225980
+2      5.06472600            24.63594933
 Ir D
-0     7.548754   46.433258
-0     7.265308   69.638074
-0     3.800969    6.150248
-0     3.718280    9.463560
+2      7.54875430            46.43325844
+2      7.26530790            69.63807366
+2      3.80096880             6.15024784
+2      3.71828010             9.46356024
 Ir F
-0     3.098706    9.483610
-0     3.049461   12.642742
+2      3.09870580             9.48360990
+2      3.04946130            12.64274211
 Ir G
-0     4.969790  -10.410697
-0     4.935614  -12.863196
+2      4.96978970           -10.41069653
+2      4.93561390           -12.86319600
 Pt nelec 60
 Pt ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Pt S
-0    14.604500  429.646087
-0     7.218287   73.156884
+2     14.60450030           429.64608700
+2      7.21828720            73.15688440
 Pt P
-0    11.577162   88.022917
-0    10.883843  175.998196
-0     6.424403   13.682274
-0     5.224198   27.414651
+2     11.57716180            88.02291727
+2     10.88384300           175.99819600
+2      6.42440290            13.68227447
+2      5.22419810            27.41465080
 Pt D
-0     7.699610   43.557852
-0     7.550808   65.369108
-0     3.961164    7.018596
-0     3.872777   11.391733
+2      7.69960960            43.55785184
+2      7.55080760            65.36910762
+2      3.96116350             7.01859592
+2      3.87277750            11.39173254
 Pt F
-0     3.379869   10.710220
-0     3.326255   14.278125
+2      3.37986900            10.71021956
+2      3.32625540            14.27812531
 Pt G
-0     5.452020  -11.651749
-0     5.412585  -14.375525
+2      5.45201960           -11.65174880
+2      5.41258490           -14.37552483
 Au nelec 60
 Au ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Au S
-0    13.523218  426.641867
-0     6.264384   36.800668
+2     13.52321800           426.64186700
+2      6.26438400            36.80066800
 Au P
-0    11.413867   87.002091
-0    10.329215  174.004370
-0     5.707424    8.870610
-0     4.828165   17.902438
+2     11.41386700            87.00209100
+2     10.32921500           174.00437000
+2      5.70742400             8.87061000
+2      4.82816500            17.90243800
 Au D
-0     7.430963   49.883655
-0     8.321990   74.684549
-0     4.609642    6.486227
-0     3.511507    9.546821
+2      7.43096300            49.88365500
+2      8.32199000            74.68454900
+2      4.60964200             6.48622700
+2      3.51150700             9.54682100
 Au F
-0     3.084639    8.791640
-0     3.024743   11.658456
+2      3.08463900             8.79164000
+2      3.02474300            11.65845600
 Au G
-0     3.978442   -5.234337
-0     4.011491   -6.738142
+2      3.97844200            -5.23433700
+2      4.01149100            -6.73814200
 Hg nelec 60
 Hg ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Hg S
-0    12.413071  275.774797
-0     6.897913   49.267898
+2     12.41307100           275.77479700
+2      6.89791300            49.26789800
 Hg P
-0    11.310320   80.506984
-0    10.210773  161.034824
-0     5.939804    9.083416
-0     5.019755   18.367773
+2     11.31032000            80.50698400
+2     10.21077300           161.03482400
+2      5.93980400             9.08341600
+2      5.01975500            18.36777300
 Hg D
-0     8.407895   51.137256
-0     8.214086   76.707459
-0     4.012612    6.561821
-0     3.795398    9.818070
+2      8.40789500            51.13725600
+2      8.21408600            76.70745900
+2      4.01261200             6.56182100
+2      3.79539800             9.81807000
 Hg F
-0     3.273106    9.429001
-0     3.208321   12.494856
+2      3.27310600             9.42900100
+2      3.20832100            12.49485600
 Hg G
-0     4.485296   -6.338414
-0     4.513200   -8.099863
+2      4.48529600            -6.33841400
+2      4.51320000            -8.09986300
 Tl nelec 60
 Tl ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Tl S
-0    12.167805  281.284663
-0     8.294909   62.434251
+2     12.16780500           281.28466300
+2      8.29490900            62.43425100
 Tl P
-0     7.151492    4.633408
-0     5.172865    9.341756
-0     9.891072   72.299253
-0     9.003391  144.558037
+2      7.15149200             4.63340800
+2      5.17286500             9.34175600
+2      9.89107200            72.29925300
+2      9.00339100           144.55803700
 Tl D
-0     7.130218   35.943039
-0     6.926906   53.909593
-0     5.417570   10.381939
-0     5.138681   15.583822
+2      7.13021800            35.94303900
+2      6.92690600            53.90959300
+2      5.41757000            10.38193900
+2      5.13868100            15.58382200
 Tl F
-0     5.626399   15.825488
-0     5.548952   21.104021
-0     2.874946    2.915127
-0     2.821451    3.896903
+2      5.62639900            15.82548800
+2      5.54895200            21.10402100
+2      2.87494600             2.91512700
+2      2.82145100             3.89690300
 Tl G
-0     6.679057   -7.494534
-0     6.706835   -9.540575
-0     7.209284   -7.797992
-0     7.070964   -9.259524
+2      6.67905700            -7.49453400
+2      6.70683500            -9.54057500
+2      7.20928400            -7.79799200
+2      7.07096400            -9.25952400
 Pb nelec 60
 Pb ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Pb S
-0    12.296303  281.285499
-0     8.632634   62.520217
+2     12.29630300           281.28549900
+2      8.63263400            62.52021700
 Pb P
-0    10.241790   72.276897
-0     8.924176  144.591083
-0     6.581342    4.758693
-0     6.255403    9.940621
+2     10.24179000            72.27689700
+2      8.92417600           144.59108300
+2      6.58134200             4.75869300
+2      6.25540300             9.94062100
 Pb D
-0     7.754336   35.848507
-0     7.720281   53.724342
-0     4.970264   10.115256
-0     4.563789   14.833731
+2      7.75433600            35.84850700
+2      7.72028100            53.72434200
+2      4.97026400            10.11525600
+2      4.56378900            14.83373100
 Pb F
-0     3.887512   12.209892
-0     3.811963   16.190291
+2      3.88751200            12.20989200
+2      3.81196300            16.19029100
 Pb G
-0     5.691577   -9.096665
-0     5.715567  -11.531996
+2      5.69157700            -9.09666500
+2      5.71556700           -11.53199600
 Bi nelec 60
 Bi ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Bi S
-0    13.043090  283.264227
-0     8.221682   62.471959
+2     13.04309000           283.26422700
+2      8.22168200            62.47195900
 Bi P
-0    10.467777   72.001499
-0     9.118901  144.002277
-0     6.754791    5.007945
-0     6.252592    9.991550
+2     10.46777700            72.00149900
+2      9.11890100           144.00227700
+2      6.75479100             5.00794500
+2      6.25259200             9.99155000
 Bi D
-0     8.081474   36.396259
-0     7.890595   54.597664
-0     4.955556    9.984294
-0     4.704559   14.981485
+2      8.08147400            36.39625900
+2      7.89059500            54.59766400
+2      4.95555600             9.98429400
+2      4.70455900            14.98148500
 Bi F
-0     4.214546   13.713383
-0     4.133400   18.194308
+2      4.21454600            13.71338300
+2      4.13340000            18.19430800
 Bi G
-0     6.205709  -10.247443
-0     6.227782  -12.955710
+2      6.20570900           -10.24744300
+2      6.22778200           -12.95571000
 Po nelec 60
 Po ul
-2     1.000000    0.000000
+2      1.00000000             0.00000000
 Po S
-0    13.277227  283.244706
-0     8.399518   62.396461
+2     13.27722700           283.24470600
+2      8.39951800            62.39646100
 Po P
-0    10.665682   71.991716
-0     9.283753  143.971871
-0     6.872749    4.949615
-0     6.326150    9.740499
+2     10.66568200            71.99171600
+2      9.28375300           143.97187100
+2      6.87274900             4.94961500
+2      6.32615000             9.74049900
 Po D
-0     8.214866   36.378383
-0     8.008696   54.562715
-0     5.055227    9.889499
-0     4.782553   14.693877
+2      8.21486600            36.37838300
+2      8.00869600            54.56271500
+2      5.05522700             9.88949900
+2      4.78255300            14.69387700
 Po F
-0     5.013270   17.428295
-0     4.984640   23.380353
-0     1.326760    0.163392
-0     1.528758    0.324566
+2      5.01327000            17.42829500
+2      4.98464000            23.38035300
+2      1.32676000             0.16339200
+2      1.52875800             0.32456600
 Po G
-0     6.771526  -11.563294
-0     6.777925  -14.509788
+2      6.77152600           -11.56329400
+2      6.77792500           -14.50978800
+At nelec 60
+At ul
+2      1.00000000             0.00000000
+At S
+2     30.20083200            49.95715800
+2     13.61230600           283.21037100
+2      8.52934000            62.28105200
+At P
+2     10.85406500            71.98237100
+2      9.46822900           143.90353200
+2      7.03111400             4.87175900
+2      6.14385800             8.98305900
+At D
+2      8.31351500            36.36323700
+2      7.99896500            54.54897000
+2      5.17996600             9.77628500
+2      4.94222600            14.26475500
+At F
+2      5.81216300            19.87019800
+2      5.75371500            26.41645200
+2      2.51347200             0.99497000
+2      2.53626100             1.49070100
+At G
+2      9.89577800           -22.22320300
+2      9.73733400           -26.71547600
+2      3.01333100            -0.37304400
+2      3.09776300            -0.48594600
+Rn nelec 60
+Rn ul
+2      1.00000000             0.00000000
+Rn S
+2     30.15124200            49.96555100
+2     14.52124100           283.07000000
+2      8.05203800            62.00287000
+Rn P
+2     11.00994200            71.96911900
+2      9.61762500           143.86055900
+2      7.33600800             4.71476100
+2      6.40625300             9.01306500
+Rn D
+2      8.36922000            36.36836500
+2      8.11697500            54.55176100
+2      5.35365600             9.63448700
+2      5.09721200            14.38790200
+Rn F
+2      6.34857100            21.79729000
+2      6.29594900            28.94680500
+2      2.88211800             1.44736500
+2      2.90804800             2.17796400
+Rn G
+2     11.01520500           -25.22809500
+2     10.90985300           -30.56612100
+2      3.48276100            -0.57480000
+2      3.60041800            -0.77953800
 END
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 8c1a8d5264..292933f6a0 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -293,6 +293,7 @@ list(
   kpoint_methods.F
   kpoint_transitional.F
   kpoint_types.F
+  libgrpp_integrals.F
   libint_2c_3c.F
   libint_wrapper.F
   library_tests.F
diff --git a/src/core_ppl.F b/src/core_ppl.F
index aa7c9351d1..76af5a807d 100644
--- a/src/core_ppl.F
+++ b/src/core_ppl.F
@@ -31,6 +31,8 @@ MODULE core_ppl
                                               sgp_potential_type
    USE kinds,                           ONLY: dp,&
                                               int_8
+   USE libgrpp_integrals,               ONLY: libgrpp_local_integral,&
+                                              libgrpp_semilocal_integral
    USE lri_environment_types,           ONLY: lri_kind_type
    USE orbital_pointers,                ONLY: init_orbital_pointers,&
                                               ncoset
@@ -123,7 +125,7 @@ CONTAINS
       INTEGER, DIMENSION(:, :), POINTER                  :: first_sgfa, first_sgfb
       INTEGER, DIMENSION(nexp_max)                       :: nct_ppl
       LOGICAL                                            :: do_dR, dokp, ecp_local, ecp_semi_local, &
-                                                            found, lpotextended
+                                                            found, lpotextended, only_gaussians
       REAL(KIND=dp)                                      :: alpha, dab, dac, dbc, f0, ppl_radius
       REAL(KIND=dp), ALLOCATABLE, DIMENSION(:, :)        :: qab, work
       REAL(KIND=dp), ALLOCATABLE, DIMENSION(:, :, :)     :: hab2_w, ppl_fwork, ppl_work
@@ -234,7 +236,7 @@ CONTAINS
 !$OMP          set_radius_a,  rpgfa, force_a, force_b, ppl_fwork, mepos, &
 !$OMP          slot, f0, katom, ppl_work, cellind, img, ecp_local, ecp_semi_local, &
 !$OMP          nloc, nrloc, aloc, bloc, n_local, a_local, c_local, &
-!$OMP          slmax, npot, nrpot, apot, bpot, &
+!$OMP          slmax, npot, nrpot, apot, bpot, only_gaussians, &
 !$OMP          ldai, hash, hash1, hash2, iatom8) &
 !$OMP REDUCTION (+ : pv_thread, force_thread )
 
@@ -382,6 +384,7 @@ CONTAINS
             CALL get_qs_kind(qs_kind_set(kkind), gth_potential=gth_potential, &
                              sgp_potential=sgp_potential)
             ecp_semi_local = .FALSE.
+            only_gaussians = .TRUE.
             IF (ASSOCIATED(gth_potential)) THEN
                CALL get_potential(potential=gth_potential, &
                                   alpha_ppl=alpha, cexp_ppl=cexp_ppl, &
@@ -409,9 +412,11 @@ CONTAINS
                   CALL get_potential(potential=sgp_potential, nloc=nloc, nrloc=nrloc, aloc=aloc, bloc=bloc)
                   nexp_ppl = nloc
                   CPASSERT(nexp_ppl <= nexp_max)
-                  nct_ppl(1:nloc) = nrloc(1:nloc) - 1
+                  nct_ppl(1:nloc) = nrloc(1:nloc)
                   alpha_ppl(1:nloc) = bloc(1:nloc)
                   cval_ppl(1, 1:nloc) = aloc(1:nloc)
+                  only_gaussians = ALL(nct_ppl(1:nloc) == 2)
+                  IF (only_gaussians) nct_ppl(1:nloc) = nct_ppl(1:nloc) - 1
                ELSE
                   CALL get_potential(potential=sgp_potential, n_local=n_local, a_local=a_local, c_local=c_local)
                   nexp_ppl = n_local
@@ -509,16 +514,37 @@ CONTAINS
                            CPABORT("Option not implemented")
                         END IF
                      ELSE
-                        CALL ppl_integral( &
-                           la_max(iset), la_min(iset), npgfa(iset), &
-                           rpgfa(:, iset), zeta(:, iset), &
-                           lb_max(jset), lb_min(jset), npgfb(jset), &
-                           rpgfb(:, jset), zetb(:, jset), &
-                           nexp_ppl, alpha_ppl, nct_ppl, cval_ppl, ppl_radius, &
-                           rab, dab, rac, dac, rbc, dbc, hab(:, :, iset, jset), ppl_work)
+                        IF (only_gaussians) THEN
+                           !If the local part of the pseudo-potential only has Gaussian functions
+                           !we can use CP2K native code, that can run without libgrpp installation
+                           CALL ppl_integral( &
+                              la_max(iset), la_min(iset), npgfa(iset), &
+                              rpgfa(:, iset), zeta(:, iset), &
+                              lb_max(jset), lb_min(jset), npgfb(jset), &
+                              rpgfb(:, jset), zetb(:, jset), &
+                              nexp_ppl, alpha_ppl, nct_ppl, cval_ppl, ppl_radius, &
+                              rab, dab, rac, dac, rbc, dbc, hab(:, :, iset, jset), ppl_work)
+
+                        ELSE
+                           !If the local part of the potential is more complex, we need libgrpp
+                           CALL libgrpp_local_integral(la_max(iset), la_min(iset), npgfa(iset), &
+                                                       rpgfa(:, iset), zeta(:, iset), &
+                                                       lb_max(jset), lb_min(jset), npgfb(jset), &
+                                                       rpgfb(:, jset), zetb(:, jset), &
+                                                       nexp_ppl, alpha_ppl, cval_ppl(1, :), nct_ppl, &
+                                                       ppl_radius, rab, dab, rac, dac, dbc, &
+                                                       hab(:, :, iset, jset))
+                        END IF
+
                         IF (ecp_semi_local) THEN
                            ! semi local ECP part
-                           CPABORT("NYA")
+                           CALL libgrpp_semilocal_integral(la_max(iset), la_min(iset), npgfa(iset), &
+                                                           rpgfa(:, iset), zeta(:, iset), &
+                                                           lb_max(jset), lb_min(jset), npgfb(jset), &
+                                                           rpgfb(:, jset), zetb(:, jset), &
+                                                           slmax, npot, bpot, apot, nrpot, &
+                                                           ppl_radius, rab, dab, rac, dac, dbc, &
+                                                           hab(:, :, iset, jset))
                         END IF
                      END IF
                   END DO
@@ -837,7 +863,7 @@ CONTAINS
                IF (SUM(ABS(aloc(1:nloc))) < 1.0e-12_dp) CYCLE
                nexp_ppl = nloc
                CPASSERT(nexp_ppl <= nexp_max)
-               nct_ppl(1:nloc) = nrloc(1:nloc) - 1
+               nct_ppl(1:nloc) = nrloc(1:nloc)
                alpha_ppl(1:nloc) = bloc(1:nloc)
                cval_ppl(1, 1:nloc) = aloc(1:nloc)
             ELSE
diff --git a/src/cp2k_info.F b/src/cp2k_info.F
index ee2f986733..c169e5356a 100644
--- a/src/cp2k_info.F
+++ b/src/cp2k_info.F
@@ -101,6 +101,9 @@ CONTAINS
 #if defined(__LIBXC)
       flags = TRIM(flags)//" libxc"
 #endif
+#if defined(__LIBGRPP)
+      flags = TRIM(flags)//" libgrpp"
+#endif
 #if defined(__LIBPEXSI)
       flags = TRIM(flags)//" pexsi"
 #endif
diff --git a/src/libgrpp_integrals.F b/src/libgrpp_integrals.F
new file mode 100644
index 0000000000..23e52d5076
--- /dev/null
+++ b/src/libgrpp_integrals.F
@@ -0,0 +1,301 @@
+!--------------------------------------------------------------------------------------------------!
+!   CP2K: A general program to perform molecular dynamics simulations                              !
+!   Copyright 2000-2023 CP2K developers group <https://cp2k.org>                                   !
+!                                                                                                  !
+!   SPDX-License-Identifier: GPL-2.0-or-later                                                      !
+!--------------------------------------------------------------------------------------------------!
+
+! **************************************************************************************************
+!> \brief Local and semi-local ECP integrals using the libgrpp library
+! **************************************************************************************************
+
+MODULE libgrpp_integrals
+   USE kinds,                           ONLY: dp
+   USE mathconstants,                   ONLY: pi
+   USE orbital_pointers,                ONLY: nco,&
+                                              ncoset
+#include "./base/base_uses.f90"
+
+   IMPLICIT NONE
+   PRIVATE
+
+   CHARACTER(len=*), PARAMETER, PRIVATE :: moduleN = 'libgrpp_integrals'
+
+   PUBLIC :: libgrpp_semilocal_integral, libgrpp_local_integral
+
+CONTAINS
+
+! **************************************************************************************************
+!> \brief Local ECP integrals using libgrpp
+!> \param la_max_set ...
+!> \param la_min_set ...
+!> \param npgfa ...
+!> \param rpgfa ...
+!> \param zeta ...
+!> \param lb_max_set ...
+!> \param lb_min_set ...
+!> \param npgfb ...
+!> \param rpgfb ...
+!> \param zetb ...
+!> \param npot_ecp ...
+!> \param alpha_ecp ...
+!> \param coeffs_ecp ...
+!> \param nrpot_ecp ...
+!> \param rpgfc ...
+!> \param rab ...
+!> \param dab ...
+!> \param rac ...
+!> \param dac ...
+!> \param dbc ...
+!> \param vab ...
+! **************************************************************************************************
+   SUBROUTINE libgrpp_local_integral(la_max_set, la_min_set, npgfa, rpgfa, zeta, &
+                                     lb_max_set, lb_min_set, npgfb, rpgfb, zetb, &
+                                     npot_ecp, alpha_ecp, coeffs_ecp, nrpot_ecp, &
+                                     rpgfc, rab, dab, rac, dac, dbc, vab)
+
+      INTEGER, INTENT(IN)                                :: la_max_set, la_min_set, npgfa
+      REAL(KIND=dp), DIMENSION(:), INTENT(IN)            :: rpgfa, zeta
+      INTEGER, INTENT(IN)                                :: lb_max_set, lb_min_set, npgfb
+      REAL(KIND=dp), DIMENSION(:), INTENT(IN)            :: rpgfb, zetb
+      INTEGER, INTENT(IN)                                :: npot_ecp
+      REAL(KIND=dp), DIMENSION(1:npot_ecp), INTENT(IN)   :: alpha_ecp, coeffs_ecp
+      INTEGER, DIMENSION(1:npot_ecp), INTENT(IN)         :: nrpot_ecp
+      REAL(KIND=dp), INTENT(IN)                          :: rpgfc
+      REAL(KIND=dp), DIMENSION(3), INTENT(IN)            :: rab
+      REAL(KIND=dp), INTENT(IN)                          :: dab
+      REAL(KIND=dp), DIMENSION(3), INTENT(IN)            :: rac
+      REAL(KIND=dp), INTENT(IN)                          :: dac
+      REAL(KIND=dp), INTENT(IN)                          :: dbc
+      REAL(KIND=dp), DIMENSION(:, :), INTENT(INOUT)      :: vab
+
+#if defined(__LIBGRPP)
+      INTEGER                                            :: a_offset, a_start, b_offset, b_start, i, &
+                                                            ipgf, j, jpgf, li, lj, ncoa, ncob
+      REAL(dp)                                           :: expi, expj, normi, normj, prefi, prefj, &
+                                                            zeti, zetj
+      REAL(dp), ALLOCATABLE, DIMENSION(:)                :: tmp
+      REAL(dp), DIMENSION(3)                             :: ra, rb, rc
+
+      !libgrpp requires absolute positions, not relative ones
+      ra(:) = 0.0_dp
+      rb(:) = rab(:)
+      rc(:) = rac(:)
+
+      DO ipgf = 1, npgfa
+         IF (rpgfa(ipgf) + rpgfc < dac) CYCLE
+         zeti = zeta(ipgf)
+         a_start = (ipgf - 1)*ncoset(la_max_set)
+
+         DO jpgf = 1, npgfb
+            IF (rpgfb(jpgf) + rpgfc < dbc) CYCLE
+            IF (rpgfa(ipgf) + rpgfb(jpgf) < dab) CYCLE
+            zetj = zetb(jpgf)
+            b_start = (jpgf - 1)*ncoset(lb_max_set)
+
+            DO li = la_min_set, la_max_set
+               a_offset = a_start + ncoset(li - 1)
+               ncoa = nco(li)
+               prefi = 2.0_dp**li*(2.0_dp/pi)**0.75_dp
+               expi = 0.25_dp*REAL(2*li + 3, dp)
+               normi = 1.0_dp/(prefi*zeti**expi)
+
+               DO lj = lb_min_set, lb_max_set
+                  b_offset = b_start + ncoset(lj - 1)
+                  ncob = nco(lj)
+                  prefj = 2.0_dp**lj*(2.0_dp/pi)**0.75_dp
+                  expj = 0.25_dp*REAL(2*lj + 3, dp)
+                  normj = 1.0_dp/(prefj*zetj**expj)
+
+                  ALLOCATE (tmp(ncoa*ncob))
+                  tmp = 0.0_dp
+                  !libgrpp implicitely normalizes cartesian Gaussian. In CP2K, we do not, hence
+                  !the 1/norm coefficients for PGFi and PGFj
+                  CALL libgrpp_type1_integrals(ra, li, 1, [normi], [zeti], &
+                                               rb, lj, 1, [normj], [zetj], &
+                                               rc, npot_ecp, nrpot_ecp, &
+                                               coeffs_ecp, alpha_ecp, tmp)
+
+                  !note: tmp array is in C row-major ordering
+                  DO j = 1, ncob
+                     DO i = 1, ncoa
+                        vab(a_offset + i, b_offset + j) = vab(a_offset + i, b_offset + j) + tmp((i - 1)*ncob + j)
+                     END DO
+                  END DO
+                  DEALLOCATE (tmp)
+
+               END DO !lj
+            END DO !li
+
+         END DO !jpgf
+      END DO !ipgf
+#else
+
+      MARK_USED(la_max_set)
+      MARK_USED(la_min_set)
+      MARK_USED(npgfa)
+      MARK_USED(rpgfa)
+      MARK_USED(zeta)
+      MARK_USED(lb_max_set)
+      MARK_USED(lb_min_set)
+      MARK_USED(npgfb)
+      MARK_USED(rpgfb)
+      MARK_USED(zetb)
+      MARK_USED(npot_ecp)
+      MARK_USED(alpha_ecp)
+      MARK_USED(coeffs_ecp)
+      MARK_USED(nrpot_ecp)
+      MARK_USED(rpgfc)
+      MARK_USED(rab)
+      MARK_USED(dab)
+      MARK_USED(rac)
+      MARK_USED(dac)
+      MARK_USED(dbc)
+      MARK_USED(vab)
+
+      CPABORT("Please compile CP2K with libgrpp support for calculations with ECPs")
+#endif
+
+   END SUBROUTINE libgrpp_local_integral
+
+! **************************************************************************************************
+!> \brief Semi-local ECP integrals using libgrpp.
+!> \param la_max_set ...
+!> \param la_min_set ...
+!> \param npgfa ...
+!> \param rpgfa ...
+!> \param zeta ...
+!> \param lb_max_set ...
+!> \param lb_min_set ...
+!> \param npgfb ...
+!> \param rpgfb ...
+!> \param zetb ...
+!> \param lmax_ecp ...
+!> \param npot_ecp ...
+!> \param alpha_ecp ...
+!> \param coeffs_ecp ...
+!> \param nrpot_ecp ...
+!> \param rpgfc ...
+!> \param rab ...
+!> \param dab ...
+!> \param rac ...
+!> \param dac ...
+!> \param dbc ...
+!> \param vab ...
+! **************************************************************************************************
+   SUBROUTINE libgrpp_semilocal_integral(la_max_set, la_min_set, npgfa, rpgfa, zeta, &
+                                         lb_max_set, lb_min_set, npgfb, rpgfb, zetb, &
+                                         lmax_ecp, npot_ecp, alpha_ecp, coeffs_ecp, nrpot_ecp, &
+                                         rpgfc, rab, dab, rac, dac, dbc, vab)
+
+      INTEGER, INTENT(IN)                                :: la_max_set, la_min_set, npgfa
+      REAL(KIND=dp), DIMENSION(:), INTENT(IN)            :: rpgfa, zeta
+      INTEGER, INTENT(IN)                                :: lb_max_set, lb_min_set, npgfb
+      REAL(KIND=dp), DIMENSION(:), INTENT(IN)            :: rpgfb, zetb
+      INTEGER, INTENT(IN)                                :: lmax_ecp
+      INTEGER, DIMENSION(0:10), INTENT(IN)               :: npot_ecp
+      REAL(KIND=dp), DIMENSION(1:15, 0:10), INTENT(IN)   :: alpha_ecp, coeffs_ecp
+      INTEGER, DIMENSION(1:15, 0:10), INTENT(IN)         :: nrpot_ecp
+      REAL(KIND=dp), INTENT(IN)                          :: rpgfc
+      REAL(KIND=dp), DIMENSION(3), INTENT(IN)            :: rab
+      REAL(KIND=dp), INTENT(IN)                          :: dab
+      REAL(KIND=dp), DIMENSION(3), INTENT(IN)            :: rac
+      REAL(KIND=dp), INTENT(IN)                          :: dac
+      REAL(KIND=dp), INTENT(IN)                          :: dbc
+      REAL(KIND=dp), DIMENSION(:, :), INTENT(INOUT)      :: vab
+
+#if defined(__LIBGRPP)
+      INTEGER                                            :: a_offset, a_start, b_offset, b_start, i, &
+                                                            ipgf, j, jpgf, li, lj, lk, ncoa, ncob
+      REAL(dp)                                           :: expi, expj, normi, normj, prefi, prefj, &
+                                                            zeti, zetj
+      REAL(dp), ALLOCATABLE, DIMENSION(:)                :: tmp
+      REAL(dp), DIMENSION(3)                             :: ra, rb, rc
+
+      !libgrpp requires absolute positions, not relative ones
+      ra(:) = 0.0_dp
+      rb(:) = rab(:)
+      rc(:) = rac(:)
+
+      DO ipgf = 1, npgfa
+         IF (rpgfa(ipgf) + rpgfc < dac) CYCLE
+         zeti = zeta(ipgf)
+         a_start = (ipgf - 1)*ncoset(la_max_set)
+
+         DO jpgf = 1, npgfb
+            IF (rpgfb(jpgf) + rpgfc < dbc) CYCLE
+            IF (rpgfa(ipgf) + rpgfb(jpgf) < dab) CYCLE
+            zetj = zetb(jpgf)
+            b_start = (jpgf - 1)*ncoset(lb_max_set)
+
+            DO li = la_min_set, la_max_set
+               a_offset = a_start + ncoset(li - 1)
+               ncoa = nco(li)
+               prefi = 2.0_dp**li*(2.0_dp/pi)**0.75_dp
+               expi = 0.25_dp*REAL(2*li + 3, dp)
+               normi = 1.0_dp/(prefi*zeti**expi)
+
+               DO lj = lb_min_set, lb_max_set
+                  b_offset = b_start + ncoset(lj - 1)
+                  ncob = nco(lj)
+                  prefj = 2.0_dp**lj*(2.0_dp/pi)**0.75_dp
+                  expj = 0.25_dp*REAL(2*lj + 3, dp)
+                  normj = 1.0_dp/(prefj*zetj**expj)
+
+                  ALLOCATE (tmp(ncoa*ncob))
+                  !Loop over ECP angular momentum
+                  DO lk = 0, lmax_ecp
+                     tmp = 0.0_dp
+                     !libgrpp implicitely normalizes cartesian Gaussian. In CP2K, we do not, hence
+                     !the 1/norm coefficients for PGFi and PGFj
+                     CALL libgrpp_type2_integrals(ra, li, 1, [normi], [zeti], &
+                                                  rb, lj, 1, [normj], [zetj], &
+                                                  rc, lk, npot_ecp(lk), nrpot_ecp(:, lk), &
+                                                  coeffs_ecp(:, lk), alpha_ecp(:, lk), tmp)
+
+                     !note: tmp array is in C row-major ordering
+                     DO j = 1, ncob
+                        DO i = 1, ncoa
+                           vab(a_offset + i, b_offset + j) = vab(a_offset + i, b_offset + j) + tmp((i - 1)*ncob + j)
+                        END DO
+                     END DO
+                  END DO !lk
+                  DEALLOCATE (tmp)
+
+               END DO !lj
+            END DO !li
+
+         END DO !jpgf
+      END DO !ipgf
+
+#else
+
+      MARK_USED(la_max_set)
+      MARK_USED(la_min_set)
+      MARK_USED(npgfa)
+      MARK_USED(rpgfa)
+      MARK_USED(zeta)
+      MARK_USED(lb_max_set)
+      MARK_USED(lb_min_set)
+      MARK_USED(npgfb)
+      MARK_USED(rpgfb)
+      MARK_USED(zetb)
+      MARK_USED(lmax_ecp)
+      MARK_USED(npot_ecp)
+      MARK_USED(alpha_ecp)
+      MARK_USED(coeffs_ecp)
+      MARK_USED(nrpot_ecp)
+      MARK_USED(rpgfc)
+      MARK_USED(rab)
+      MARK_USED(dab)
+      MARK_USED(rac)
+      MARK_USED(dac)
+      MARK_USED(dbc)
+      MARK_USED(vab)
+
+      CPABORT("Please compile CP2K with libgrpp support for calculations with ECPs")
+#endif
+
+   END SUBROUTINE libgrpp_semilocal_integral
+
+END MODULE libgrpp_integrals
diff --git a/src/qs_kind_types.F b/src/qs_kind_types.F
index b8c34ec2ea..1757a5216b 100644
--- a/src/qs_kind_types.F
+++ b/src/qs_kind_types.F
@@ -2362,6 +2362,7 @@ CONTAINS
                                      npot=ecppot%npot, nrpot=ecppot%nrpot, apot=ecppot%apot, bpot=ecppot%bpot)
                   ! convert PP
                   IF (.NOT. ecp_semi_local) THEN
+                     CPABORT("ECPs are only well tested in their semi-local form")
                      CALL get_qs_kind(qs_kind, basis_set=orb_basis_set)
                      CALL sgp_construction(sgp_pot=sgppot, ecp_pot=ecppot, orb_basis=orb_basis_set, error=error)
                      IF (iounit > 0) THEN
diff --git a/tests/QS/regtest-ecp/ECP_BASIS_POT b/tests/QS/regtest-ecp/ECP_BASIS_POT
new file mode 100644
index 0000000000..de04364c09
--- /dev/null
+++ b/tests/QS/regtest-ecp/ECP_BASIS_POT
@@ -0,0 +1,203 @@
+#----------------------------------------------------------------------
+# Basis Set Exchange
+# Version v0.9.1
+# https://www.basissetexchange.org
+#----------------------------------------------------------------------
+#   Basis set: CRENBL
+# Description: CRENBL designed for use with small core potentials
+#        Role: orbital
+#     Version: 0  (Data from the Original Basis Set Exchange)
+#----------------------------------------------------------------------
+
+# Radon Stuttgart RLC (4s,4p,1d) -> [2s,2p,1d]
+Rn Stuttgart-RLC
+    5
+1 0 0 3 1
+      1.9783250              0.6789880
+      1.5140330             -1.1841590
+      0.3246540              0.9210860
+1 0 0 1 1
+      0.1273660              1.0000000
+1 1 1 3 1
+      2.0310950              0.2320400
+      1.6561220             -0.3545180
+      0.2983650              0.6651200
+1 1 1 1 1
+      0.1032220              1.0000000
+1 2 2 1 1
+      0.2600000              1.0000000
+
+## Effective core potentials
+Stuttgart_RLC_ECP
+Rn nelec 78
+Rn ul
+2      1.000000000            0.000000000
+Rn S
+2      0.922386000           -5.019005000
+2      1.781915000           37.036790000
+2     10.804601000          195.103308000
+Rn P
+2      0.724291000           -1.966481000
+2      1.363860000           23.464059000
+Rn D
+2      0.769400000            7.483457000
+2      1.538800000            9.361900000
+Rn F
+2      1.213897000           -6.763150000
+Rn G
+2      1.576469000           -9.915662000
+END Stuttgart_RLC_ECP
+
+# Hydrogen def2-SVP (4s,1p) -> [2s,1p]
+H def2-SVP
+    3
+1 0 0 3 1
+     13.0107010              0.19682158E-01
+      1.9622572              0.13796524
+      0.44453796             0.47831935
+1 0 0 1 1
+      0.12194962             1.0000000
+1 1 1 1 1
+      0.8000000              1.0000000
+
+# Antimony def2-SVP (10s,7p,6d) -> [4s,4p,2d]
+Sb def2-SVP
+    10
+1 0 0 2 1
+     10.584496987           -0.14845336778E-01
+      1.4680242769           0.35289492025
+1 0 0 6 1
+    372.76139166             0.15878057239E-02
+     22.689478596           -0.15027605583
+     18.391547037            0.35915813039
+      7.6406271414          -0.74805091065
+      1.9052000235           0.92017581656
+      0.93007107773          0.46754079597
+1 0 0 1 1
+      0.21621190032          1.0000000
+1 0 0 1 1
+      0.83546307041E-01      1.0000000
+1 1 1 1 1
+      2.6190751238           1.0000000
+1 1 1 4 1
+     15.926550950            0.13206950012
+     10.052739237           -0.41511149340
+      1.2682183726           0.74197972626
+      0.57196620929          0.15580772750
+1 1 1 1 1
+      0.25183282652          1.0000000
+1 1 1 1 1
+      0.83389127684E-01      1.0000000
+1 2 2 5 1
+     45.485063360            0.32556415807E-02
+     18.504059617           -0.54952972010E-02
+      3.9156032308           0.27988806353
+      1.7142196009           0.51273377761
+      0.69675478242          0.33288802736
+1 2 2 1 1
+      0.23060000000          1.0000000
+
+## Effective core potentials
+def2-SVP_ECP
+Sb nelec 28
+Sb ul
+2     14.44497800           -15.36680100
+2     14.44929500           -20.29613800
+Sb S
+2     16.33086500           281.07158100
+2      8.55654200            61.71660400
+2     14.44497800            15.36680100
+2     14.44929500            20.29613800
+Sb P
+2     14.47033700            67.45738000
+2     13.81619400           134.93350300
+2      8.42492400            14.71634400
+2      8.09272800            29.51851200
+2     14.44497800            15.36680100
+2     14.44929500            20.29613800
+Sb D
+2     14.88633100            35.44781500
+2     15.14631900            53.14346600
+2      5.90826700             9.17922300
+2      5.59432200            13.24025300
+2     14.44497800            15.36680100
+2     14.44929500            20.29613800
+END def2-SVP_ECP
+
+## All-electron potential
+H ALLELECTRON ALL
+    1    0    0
+     0.20000000    0
+
+# Chlorine LANL2DZ (3s,3p) -> [2s,2p]
+Cl LANL2DZ
+    2
+1 0 0 3 2
+      2.2310000             -0.4900589              0.0000000
+      0.4720000              1.2542684              0.0000000
+      0.1631000              0.0000000              1.0000000
+1 1 1 3 2
+      6.2960000             -0.0635641              0.0000000
+      0.6333000              1.0141355              0.0000000
+      0.1819000              0.0000000              1.0000000
+
+# Iodine LANL2DZ (3s,3p) -> [2s,2p]
+I LANL2DZ
+    2
+1 0 0 3 2
+      0.7242000             -2.9731048              0.0000000
+      0.4653000              3.4827643              0.0000000
+      0.1336000              0.0000000              1.0000000
+1 1 1 3 2
+      1.2900000             -0.2092377              0.0000000
+      0.3180000              1.1035347              0.0000000
+      0.1053000              0.0000000              1.0000000
+
+## Effective core potentials
+LANL2DZ_ECP
+Cl nelec 10
+Cl ul
+1     94.8130000            -10.0000000
+2    165.6440000             66.2729170
+2     30.8317000            -28.9685950
+2     10.5841000            -12.8663370
+2      3.7704000             -1.7102170
+Cl S
+0    128.8391000              3.0000000
+1    120.3786000             12.8528510
+2     63.5622000            275.6723980
+2     18.0695000            115.6777120
+2      3.8142000             35.0606090
+Cl P
+0    216.5263000              5.0000000
+1     46.5723000              7.4794860
+2    147.4685000            613.0320000
+2     48.9869000            280.8006850
+2     13.2096000            107.8788240
+2      3.1831000             15.3439560
+I nelec 46
+I ul
+0      1.0715702             -0.0747621
+1     44.1936028            -30.0811224
+2     12.9367609            -75.3722721
+2      3.1956412            -22.0563758
+2      0.8589806             -1.6979585
+I S
+0    127.9202670              2.9380036
+1     78.6211465             41.2471267
+2     36.5146237            287.8680095
+2      9.9065681            114.3758506
+2      1.9420086             37.6547714
+I P
+0     13.0035304              2.2222630
+1     76.0331404             39.4090831
+2     24.1961684            177.4075002
+2      6.4053433             77.9889462
+2      1.5851786             25.7547641
+I D
+0     40.4278108              7.0524360
+1     28.9084375             33.3041635
+2     15.6268936            186.9453875
+2      4.1442856             71.9688361
+2      0.9377235              9.3630657
+END LANL2DZ_ECP
diff --git a/tests/QS/regtest-ecp/ICl_lanl2dz_gpw.inp b/tests/QS/regtest-ecp/ICl_lanl2dz_gpw.inp
new file mode 100644
index 0000000000..a37c3980b6
--- /dev/null
+++ b/tests/QS/regtest-ecp/ICl_lanl2dz_gpw.inp
@@ -0,0 +1,58 @@
+&GLOBAL
+  PROJECT ICl_lanl2dz_gpw
+  RUN_TYPE ENERGY
+&END GLOBAL
+&FORCE_EVAL
+  &DFT
+    BASIS_SET_FILE_NAME ./ECP_BASIS_POT
+    POTENTIAL_FILE_NAME ./ECP_BASIS_POT
+
+    &QS
+      METHOD GPW
+      EPS_DEFAULT 1.0E-12
+    &END QS
+
+    &SCF
+      SCF_GUESS ATOMIC
+      MAX_SCF 5
+    &END
+
+    &MGRID
+      CUTOFF 400
+      REL_CUTOFF 40
+      NGRIDS 5
+    &END
+
+    &POISSON
+      PERIODIC NONE
+      PSOLVER WAVELET
+    &END
+
+    &XC
+      &XC_FUNCTIONAL LDA
+      &END XC_FUNCTIONAL
+    &END XC
+  &END DFT
+  &SUBSYS
+    &CELL
+      ABC  10.0  10.0  10.0
+      PERIODIC NONE
+    &END CELL
+    &COORD
+      Cl  0.00000    0.00000     0.00000
+      I   0.00000    0.00000     2.49000
+    &END COORD
+    &TOPOLOGY
+      &CENTER_COORDINATES
+      &END
+    &END
+    &KIND I
+      BASIS_SET LANL2DZ
+      POTENTIAL ECP LANL2DZ_ECP
+    &END KIND
+    &KIND Cl
+      BASIS_SET LANL2DZ
+      POTENTIAL ECP LANL2DZ_ECP
+    &END KIND
+  &END SUBSYS
+&END FORCE_EVAL
diff --git a/tests/QS/regtest-ecp/Rn_stuttgart_gapw.inp b/tests/QS/regtest-ecp/Rn_stuttgart_gapw.inp
new file mode 100644
index 0000000000..cf3e79ddcb
--- /dev/null
+++ b/tests/QS/regtest-ecp/Rn_stuttgart_gapw.inp
@@ -0,0 +1,44 @@
+&GLOBAL
+  PROJECT Rn_stuttgart_gapw
+  RUN_TYPE ENERGY
+&END GLOBAL
+&FORCE_EVAL
+  &DFT
+    BASIS_SET_FILE_NAME ./ECP_BASIS_POT
+    POTENTIAL_FILE_NAME ./ECP_BASIS_POT
+
+    &QS
+      METHOD GAPW
+      EPS_DEFAULT 1.0E-12
+    &END QS
+
+    &SCF
+      SCF_GUESS ATOMIC
+      MAX_SCF 5
+    &END
+
+    &MGRID
+      CUTOFF 400
+      REL_CUTOFF 40
+      NGRIDS 5
+    &END
+
+    &XC
+      &XC_FUNCTIONAL LDA
+      &END XC_FUNCTIONAL
+    &END XC
+  &END DFT
+  &SUBSYS
+    &CELL
+      ABC  5.0  5.0  10.0
+    &END CELL
+    &COORD
+      Rn  0.00000    0.00000     0.00000
+      Rn  0.00000    0.00000     5.00000
+    &END COORD
+    &KIND Rn
+      BASIS_SET Stuttgart-RLC
+      POTENTIAL ECP Stuttgart_RLC_ECP
+    &END KIND
+  &END SUBSYS
+&END FORCE_EVAL
diff --git a/tests/QS/regtest-ecp/SbH3_def2_gapw.inp b/tests/QS/regtest-ecp/SbH3_def2_gapw.inp
new file mode 100644
index 0000000000..e25b501ec8
--- /dev/null
+++ b/tests/QS/regtest-ecp/SbH3_def2_gapw.inp
@@ -0,0 +1,60 @@
+&GLOBAL
+  PROJECT SbH3_def2_gapw
+  RUN_TYPE ENERGY
+&END GLOBAL
+&FORCE_EVAL
+  &DFT
+    BASIS_SET_FILE_NAME ./ECP_BASIS_POT
+    POTENTIAL_FILE_NAME ./ECP_BASIS_POT
+
+    &QS
+      METHOD GAPW
+      EPS_DEFAULT 1.0E-12
+    &END QS
+
+    &SCF
+      SCF_GUESS ATOMIC
+      MAX_SCF 5
+    &END
+
+    &MGRID
+      CUTOFF 400
+      REL_CUTOFF 40
+      NGRIDS 5
+    &END
+
+    &POISSON
+      PERIODIC NONE
+      PSOLVER WAVELET
+    &END
+
+    &XC
+      &XC_FUNCTIONAL LDA
+      &END XC_FUNCTIONAL
+    &END XC
+  &END DFT
+  &SUBSYS
+    &CELL
+      ABC  10.0  10.0  10.0
+      PERIODIC NONE
+    &END CELL
+    &COORD
+      Sb        0.0000000000       -0.2357770000       -0.6270200000 
+      H         0.0000000000        1.1518460000        0.3391280000
+      H        -1.2017170000       -0.9295890000        0.3391280000
+      H         0.2017170000       -0.9295890000        0.3391280000
+    &END COORD
+    &TOPOLOGY
+      &CENTER_COORDINATES
+      &END
+    &END
+    &KIND Sb
+      BASIS_SET def2-SVP
+      POTENTIAL ECP def2-SVP_ECP
+    &END KIND
+    &KIND H
+      BASIS_SET def2-SVP
+      POTENTIAL ALL
+    &END KIND
+  &END SUBSYS
+&END FORCE_EVAL
diff --git a/tests/QS/regtest-ecp/TEST_FILES b/tests/QS/regtest-ecp/TEST_FILES
new file mode 100644
index 0000000000..e2a3f2a10d
--- /dev/null
+++ b/tests/QS/regtest-ecp/TEST_FILES
@@ -0,0 +1,3 @@
+ICl_lanl2dz_gpw.inp                                      11   1.0E-11              -23.515911094537550
+Rn_stuttgart_gapw.inp                                    11   1.0E-11              -25.632304810373267
+SbH3_def2_gapw.inp                                       11   1.0E-11             -212.357670903187426
diff --git a/tests/TEST_DIRS b/tests/TEST_DIRS
index c4cca532c4..e6fd2b36b9 100644
--- a/tests/TEST_DIRS
+++ b/tests/TEST_DIRS
@@ -3,6 +3,7 @@
 # Directories have been reordered according the execution time needed for a gfortran pdbg run using 2 MPI tasks
 # in case a new directory is added just add it at the top of the list..
 # the order will be regularly checked and modified...
+QS/regtest-ecp                                              libgrpp
 QS/regtest-as-3                                             libint mpiranks%2==0
 QS/regtest-as-2                                             libint
 QS/regtest-wfn-restart
diff --git a/tools/toolchain/install_cp2k_toolchain.sh b/tools/toolchain/install_cp2k_toolchain.sh
index 9255b29ee0..957fe85c0c 100755
--- a/tools/toolchain/install_cp2k_toolchain.sh
+++ b/tools/toolchain/install_cp2k_toolchain.sh
@@ -170,6 +170,9 @@ The --with-PKG options follow the rules:
   --with-libint           libint, library for evaluation of two-body molecular
                           integrals, needed for hybrid functional calculations
                           Default = install
+  --with-libgrpp          libgrpp, library for the evaluation of ECP integrals, needed
+                          for any calculations with semi-local ECP pseudopotentials 
+                          Default = install
   --with-fftw             FFTW3, library for fast fourier transform
                           Default = install
   --with-acml             AMD core maths library, which provides LAPACK and BLAS
@@ -259,7 +262,7 @@ EOF
 tool_list="gcc intel cmake"
 mpi_list="mpich openmpi intelmpi"
 math_list="mkl acml openblas"
-lib_list="fftw libint libxc libxsmm cosma scalapack elpa cusolvermp plumed \
+lib_list="fftw libint libxc libgrpp libxsmm cosma scalapack elpa cusolvermp plumed \
           spfft spla ptscotch superlu pexsi quip gsl spglib hdf5 libvdwxc sirius
           libvori libtorch"
 package_list="${tool_list} ${mpi_list} ${math_list} ${lib_list}"
@@ -280,6 +283,7 @@ with_gcc="__SYSTEM__"
 # libs to turn on by default, the math and mpi libraries are chosen by there respective modes:
 with_fftw="__INSTALL__"
 with_libint="__INSTALL__"
+with_libgrpp="__INSTALL__"
 with_libxsmm="__INSTALL__"
 with_libxc="__INSTALL__"
 with_scalapack="__INSTALL__"
@@ -560,6 +564,9 @@ while [ $# -ge 1 ]; do
     --with-libxc*)
       with_libxc=$(read_with "${1}")
       ;;
+    --with-libgrpp*)
+      with_libgrpp=$(read_with "${1}")
+      ;;
     --with-fftw*)
       with_fftw=$(read_with "${1}")
       ;;
diff --git a/tools/toolchain/scripts/stage3/install_libgrpp.sh b/tools/toolchain/scripts/stage3/install_libgrpp.sh
new file mode 100755
index 0000000000..cf8e51b981
--- /dev/null
+++ b/tools/toolchain/scripts/stage3/install_libgrpp.sh
@@ -0,0 +1,108 @@
+#!/bin/bash -e
+
+# TODO: Review and if possible fix shellcheck errors.
+# shellcheck disable=all
+
+[ "${BASH_SOURCE[0]}" ] && SCRIPT_NAME="${BASH_SOURCE[0]}" || SCRIPT_NAME=$0
+SCRIPT_DIR="$(cd "$(dirname "$SCRIPT_NAME")/.." && pwd -P)"
+
+libgrpp_ver="20231206"
+libgrpp_sha="85c8caeca62589ca4e23709f467fd65e49079c0720f4db78f4382ce91cc3cebc"
+source "${SCRIPT_DIR}"/common_vars.sh
+source "${SCRIPT_DIR}"/tool_kit.sh
+source "${SCRIPT_DIR}"/signal_trap.sh
+source "${INSTALLDIR}"/toolchain.conf
+source "${INSTALLDIR}"/toolchain.env
+
+[ -f "${BUILDDIR}/setup_libgrpp" ] && rm "${BUILDDIR}/setup_libgrpp"
+
+LIBGRPP_CFLAGS=""
+LIBGRPP_LDFLAGS=""
+LIBGRPP_LIBS=""
+! [ -d "${BUILDDIR}" ] && mkdir -p "${BUILDDIR}"
+cd "${BUILDDIR}"
+
+case "$with_libgrpp" in
+  __INSTALL__)
+    echo "==================== Installing libgrpp ===================="
+    pkg_install_dir="${INSTALLDIR}/libgrpp-main-${libgrpp_ver}"
+    echo "pkg_install_dir:"
+    echo ${pkg_install_dir}
+    install_lock_file="$pkg_install_dir/install_successful"
+    if verify_checksums "${install_lock_file}"; then
+      echo "libgrpp-main-${libgrpp_ver} is already installed, skipping it."
+    else
+      if [ -f libgrpp-${libgrpp_ver}.zip ]; then
+        echo "libgrpp-main-${libgrpp_ver}.zip is found"
+      else
+        download_pkg_from_cp2k_org "${libgrpp_sha}" "libgrpp-main-${libgrpp_ver}.zip"
+      fi
+      echo "Installing from scratch into ${pkg_install_dir}"
+      [ -d libgrpp-main-${libgrpp_ver} ] && rm -rf libgrpp-main-${libgrpp_ver}
+      unzip -qq libgrpp-main-${libgrpp_ver}.zip
+      cd libgrpp-main
+
+      mkdir build
+      cd build
+      CC=${CC} FC=${FC} cmake .. > cmake.log 2>&1 || tail -n ${LOG_LINES} cmake.log
+      make > make.log 2>&1 || tail -n ${LOG_LINES} make.log
+      cd ..
+
+      install -d "${pkg_install_dir}/lib" >> install.log 2>&1
+      install -d "${pkg_install_dir}/include" >> install.log 2>&1
+      install -m 644 build/libgrpp/liblibgrpp.a "${pkg_install_dir}/lib" >> install.log 2>&1
+      install -m 644 libgrpp/* "${pkg_install_dir}/include" >> install.log 2>&1
+
+      cd ..
+      write_checksums "${install_lock_file}" "${SCRIPT_DIR}/stage3/$(basename ${SCRIPT_NAME})"
+    fi
+
+    LIBGRPP_CFLAGS="-I'${pkg_install_dir}/include'"
+    LIBGRPP_LDFLAGS="-L'${pkg_install_dir}/lib' -Wl,-rpath,'${pkg_install_dir}/lib'"
+    ;;
+  __SYSTEM__)
+    echo "==================== Finding libgrpp from system paths ===================="
+    check_lib -llibgrpp "libgrpp"
+    add_include_from_paths -p LIBGRPP_CFLAGS "libgrpp" $INCLUDE_PATHS
+    add_lib_from_paths LIBGRPP_LDFLAGS "liblibgrpp.*" $LIB_PATHS
+    ;;
+  __DONTUSE__) ;;
+
+  *)
+    echo "==================== Linking libgrpp to user paths ===================="
+    pkg_install_dir="$with_libgrpp"
+    check_dir "${pkg_install_dir}/include"
+    check_dir "${pkg_install_dir}/lib"
+    LIBGRPP_CFLAGS="-I'${pkg_install_dir}/include'"
+    LIBGRPP_LDFLAGS="-L'${pkg_install_dir}/lib'"
+    ;;
+esac
+if [ "$with_libgrpp" != "__DONTUSE__" ]; then
+  LIBGRPP_LIBS="-llibgrpp"
+  if [ "$with_libgrpp" != "__SYSTEM__" ]; then
+    cat << EOF > "${BUILDDIR}/setup_libgrpp"
+prepend_path LD_LIBRARY_PATH "$pkg_install_dir/lib"
+prepend_path LD_RUN_PATH "$pkg_install_dir/lib"
+prepend_path LIBRARY_PATH "$pkg_install_dir/lib"
+prepend_path PKG_CONFIG_PATH "$pkg_install_dir/lib/pkgconfig"
+prepend_path CMAKE_PREFIX_PATH "$pkg_install_dir"
+export LIBGRPP_ROOT="${pkg_install_dir}"
+EOF
+    cat "${BUILDDIR}/setup_libgrpp" >> $SETUPFILE
+  fi
+  cat << EOF >> "${BUILDDIR}/setup_libgrpp"
+export LIBGRPP_CFLAGS="${LIBGRPP_CFLAGS}"
+export LIBGRPP_LDFLAGS="${LIBGRPP_LDFLAGS}"
+export LIBGRPP_LIBS="${LIBGRPP_LIBS}"
+export CP_DFLAGS="\${CP_DFLAGS} -D__LIBGRPP"
+export CP_CFLAGS="\${CP_CFLAGS} ${LIBGRPP_CFLAGS}"
+export CP_LDFLAGS="\${CP_LDFLAGS} ${LIBGRPP_LDFLAGS}"
+export CP_LIBS="${LIBGRPP_LIBS} \${CP_LIBS}"
+EOF
+fi
+
+load "${BUILDDIR}/setup_libgrpp"
+write_toolchain_env "${INSTALLDIR}"
+
+cd "${ROOTDIR}"
+report_timing "libgrpp"
diff --git a/tools/toolchain/scripts/stage3/install_stage3.sh b/tools/toolchain/scripts/stage3/install_stage3.sh
index 5a77901695..a25e37edff 100755
--- a/tools/toolchain/scripts/stage3/install_stage3.sh
+++ b/tools/toolchain/scripts/stage3/install_stage3.sh
@@ -6,5 +6,6 @@
 ./scripts/stage3/install_fftw.sh
 ./scripts/stage3/install_libint.sh
 ./scripts/stage3/install_libxc.sh
+./scripts/stage3/install_libgrpp.sh
 
 #EOF