Manual: Migrate howto:ipi from wiki (Orig. Author: Jinggang Lan)

docs/methods/sampling/i-pi.md

@@ -0,0 +1,123 @@
+# i-PI
+
+i-PI is a Python interface for ab initio path integral molecular dynamics simulations. i-PI is
+composed of a Python server (i-pi itself, that does not need to be compiled but only requires a
+relatively recent version of Python and Numpy) that propagates the (path integral) dynamics of the
+nuclei, and of an external code that acts as a client and computes the electronic energy and forces.
+
+The i-PI documentation can be found at <https://ipi-code.org>.
+
+Please cite [](#Kapil2016) and [Kapil2018](https://doi.org/10.1016/j.cpc.2018.09.020) if you use
+i-PI with CP2K.
+
+Published work using i-PI with CP2K:
+
+- [J. Phys. Chem. Lett. 2020, 11, 9, 3724–3730](https://doi.org/10.1021/acs.jpclett.0c01025)
+- [PNAS 01, 22, 2019 116 (4) 1110-1115](https://doi.org/10.1073/pnas.1815117116)
+- [Nature Communications 12, 766 (2021)](https://doi.org/10.1038/s41467-021-20914-0)
+
+## Download i-PI from Github
+
+```none
+git clone https://github.com/i-pi/i-pi.git
+```
+
+To run i-PI, one need to source the environment file from the i-PI directory
+
+```none
+source ${PATH_TO_IPI}/env.sh
+```
+
+Then one can run i-PI by using
+
+```none
+i-pi input.xml > log &
+```
+
+There are many input examples in
+[i-pi examples folder](https://github.com/i-pi/i-pi/tree/master/examples), which contains different
+methods, e.g. NVE, NVT, NPT, PIMD, REMP, etc.
+
+## Run i-PI with INET socket
+
+To use CP2K as the client code using an **internet** domain socket on the
+[HOST](#CP2K_INPUT.MOTION.DRIVER.HOST) address “host_address” and on the
+[PORT](#CP2K_INPUT.MOTION.DRIVER.PORT) number “port” the following lines must be added to its input
+file:
+
+```none
+&MOTION
+...
+   &DRIVER
+      HOST host_address
+      PORT port
+   &END DRIVER
+...
+&END MOTION
+```
+
+In the `input.xml`, one need to use the same host_address and port to CP2K input.
+
+```none
+<ffsocket mode='inet' name='driver'>
+  <address>host_address</address>
+  <port>port</port>
+  <latency>0.01</latency>
+  <timeout>5000</timeout>
+</ffsocket>
+```
+
+## Run i-PI with UNIX socket
+
+If instead a [UNIX](#CP2K_INPUT.MOTION.DRIVER.UNIX) domain socket is required then the following
+modification is necessary:
+
+```none
+&MOTION
+...
+   &DRIVER
+      HOST host_address
+      PORT port
+      UNIX
+   &END DRIVER
+   ...
+&END MOTION
+```
+
+In the **input.xml**, one to specify the mode=unix to enable the communication via UNIX socket.
+
+```none
+<ffsocket mode='unix' name='driver'>
+  <address>host_address</address>
+  <port>port</port>
+  <latency>0.01</latency>
+  <timeout>5000</timeout>
+</ffsocket>
+```
+
+## Run I-PI with CP2K on a supercomputer
+
+To run I-PI with CP2K on a supercomputer is also straightforward, one needs to get the hostname
+where the i-PI is executed, and then replace this variable in the CP2K input files. Here is an
+example script one can use to run I-PI with CP2K on the Daint machine (CSCS).
+
+```bash
+HOST=$(hostname)
+
+source ~/i-pi/env.sh
+
+if [ -e simulation.restart ]; then
+   sed -i "s/address>[^<]*</address>$HOST</" simulation.restart
+   i-pi simulation.restart  >> log.ipi 2>&1 &
+else
+   sed -i "s/address>[^<]*</address>$HOST</" input.xml
+   i-pi input.xml &> log.ipi &
+fi
+sleep 5
+
+sed -i "s/HOST.*/HOST $HOST/" cp2k.inp
+
+srun cp2k.psmp -i cp2k.inp -o cp2k.out
+
+wait
+```

docs/methods/sampling/index.md

@@ -9,7 +9,7 @@ molecular_dynamics
 metadynamics
 path_integrals
 newton-x
-i-PI <https://www.cp2k.org/howto:ipi>
+i-pi
 Gibbs Ensemble Monte Carlo <https://www.cp2k.org/howto:gemc>
 Langevin Dynamics <https://www.cp2k.org/howto:langevin_regions>
 ehrenfest