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<HEAD><TITLE>scf benchmarks</TITLE></HEAD>
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<BODY BACKGROUND="../../backgrounds/zsm.gif" BGCOLOR="FAEBD7">
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<UL>
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<LI><A HREF="../index.html">Return to NWChem benchmarks</A>
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<LI><A HREF="../../nwchem.html">Return to NWChem home page</A>
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</LI></UL><HR>
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<H1>Massively-Parallel Self-Consistent Field Benchmarks</H1>
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<P><I>The scaling of the distributed-data SCF is illustrated,
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including some very fast in-core calculations on the CRAY-T3D (e.g.,
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the total time for a 324 function, DZP basis, SCF on <I>C14F6H8</I> is
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just 5.5 minutes). The excellent scaling of large in-core
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calculations also proves that the direct algorithm will benefit fully
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from the introduction of faster integral technology into NWChem.</I>
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<H2>Background</H2>
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<P>As part of our <A HREF="../../hpcci/hpcci.html">High-Performance
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Computing and Communications Collaboration</A> we have collected a set
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of benchmark calculations to use to help in establishing design goals
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and in tracking performance. A paper is in preparation which compares
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the performance of NWChem with other computational chemistry packages
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on a variety of parallel computers. The current document picks out
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certain interesting highlights.
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<H2><I>Si108O194H81C5N</I> - zeolite fragment</H2>
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<UL>
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<LI> 2053 functions, minimal basis
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<LI> 389 atoms, no symmetry
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</UL>
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<P>This system was of interest to PNNL researchers as an early
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cluster model for reactions inside minerals. It is a fragment of the
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zeolite ZSM-5, terminated with hydrogen atoms and with an embedded
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pyridine molecule. The high sparsity and small basis caused
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the previous version of NWChem to spend most of its time accessing
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global arrays, but the current version spends less than 1.6% of the
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time in global array accesses (CRAY-T3D, 256 nodes).
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<P>This calculation would not be possible with a replicated-data
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algorithm on many massively parallel computers since the Fock and
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density matrices require at least 34 Mbytes (storing lower triangular
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matrices). The distributed-data algorithm requires just 0.26
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Mbytes/node (on 256 processors, storing full square matrices) leaving
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much more memory to optimize the speed of integral evaluation.
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<P>The following table presents wall times in hours for complete
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SCF calculations on this system on several parallel computers. The
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SP1 at Argonne National Laboratory is unusual since it has
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SP1 compute nodes but uses an SP2 switch.
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<PRE>
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No. of
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proc.s T3D KSR2 SP1
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------ --- ---- ---
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64 - - 5
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72 - 4.4 -
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128 2.9 - -
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</PRE>
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<H2><I>C14F6H8</I></H2>
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<UL>
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<LI> 324 functions, C(3s2p1d), F(3s2p1d), H(3s)
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<LI> 28 atoms, no symmetry
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</UL>
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<P>This medium-sized molecule is representative of many routine
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calculations and is also about the largest molecule without symmetry
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for which it is practical to cache all integrals in memory. The
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combination of massive parallelism and in-core algorithm makes for
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very high performance. The distributed data method makes over 200
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Mbytes more memory available for caching integrals than would be
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available using a replicated-data approach.
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<P>The following table presents total wall times in <I>seconds</I>
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for a complete SCF calculation on this system using a fully in-core
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algorithm on the NERSC CRAY-T3D which has 64 Mbytes of memory per
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node.
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<PRE>
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T3D
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Processors New (in-core)
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---------- -------------
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128 605
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256 334
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</PRE>
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<H2><I>(Cp)Co(NO)(CH3)</I></H2>
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<UL>
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<LI> 114 function, minimal basis
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<LI> 17 atoms, <I>Cs</I> symmetry
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</UL>
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<P>This cluster was provided by our industrial collaborators as being
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representative of systems being considered as catalysts. Due to bugs,
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previous versions of NWChem obtained only first-order convergence for
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this system. This problem has been addressed and full, stable
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second-order convergence is now obtained. In addition, <A
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HREF="ddscf.html">optimizations in the use of linear algebra</A> has
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significantly improved the scalability of this calculation.
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<P> The following table presents total wall time in minutes for this
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problem for the old and new versions of the code running on the KSR-2
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and CRAY T3D. The drop-off in performance is typical for small
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molecules and is due to poor load-balancing - the cobalt atom has
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many more functions on it than the other atoms. The performance could be
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enhanced by splitting large atoms, but this is only necessary for small
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molecules.
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<PRE>
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KSR T3D
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------------------------- -------------------------
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No. of Old New New Old New New
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proc.s Direct Direct In-core Direct Direct In-core
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------ ------ ------ ------- ------ ------ -------
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1 - 406.0 - - - -
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8 - 53.2 7.5 - - -
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16 38.0 29.6 4.5 - 31.0 -
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32 31.8* 18.8 2.9 23 17.7 2.3
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64 21.3** 12.3 2.8 15 10.9 -
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128 - - - 11 7.9 -
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* = 36 processor time
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** = 72 processor time
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</PRE>
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<H2>Acknowledgments</H2>
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This work was performed under the auspices of the High Performance
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Computing and Communications Program of the Office of Scientific
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Computing, U.S. Department of Energy under contract DE-AC6-76RLO 1830
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with Battelle Memorial Institute which operates the Pacific Northwest
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National Laboratory, a multiprogram national laboratory. This work
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has made extensive use of software developed by the Molecular Science
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Software Group of the Environmental Molecular Sciences Laboratory
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project managed by the Office Health and Energy Research.
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This research was performed in part using the Caltech Concurrent
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Supercomputing Facilities (CCSF) operated by Caltech on behalf of the
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Concurrent Supercomputing Consortium. Access to this facility was
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provided by Pacific Northwest National Laboratory.
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<P>
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<HR>
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<ADDRESS>Prepared by RJ Harrison: Email: nwchem-support@emsl.pnl.gov.</ADDRESS>
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