This a short tutorial on how to run I-PI with CP2K.
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 manual can be found in i-PI Manual
Please cite Computer Physics Communications 236 (2019) 214–223 and J. Chem. Phys. 144, 054111 (2016) if you use I-PI with CP2K.
Published work using I-PI with CP2K:
J. Phys. Chem. Lett. 2020, 11, 9, 3724–3730
PNAS 01, 22, 2019 116 (4) 1110-1115
Nature Communications 12, 766 (2021)
Download i-PI from Github
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
source ${PATH_TO_IPI}/env.sh
Then one can run i-PI by using
i-pi input.xml > log &
There are many input examples in i-pi/examples/ folder, which contains different methods, e.g. NVE, NVT, NPT, PIMD, REMP, etc.
Run i-PI with INET socket
To use CP2K as the client code using an internet domain socket on the host address “host_address” and on the port number “port” the following lines must be added to its input file:
&MOTION
...
&DRIVER
HOST host_address
PORT port
&END DRIVER
...
&END MOTION
In the input.xml, one need to use the same host_address and port to CP2K input.
<ffsocket mode='inet' name='driver'>
<address>host_address</address>
<port>port</port>
<latency>0.01</latency>
<timeout>5000</timeout>
</ffsocket>
Run i-PI with UNIX socket
If instead a unix domain socket is required then the following modification is necessary:
&MOTION
...
&DRIVER
HOST host_address
PORT port
UNIX
&END DRIVER
...
&END MOTION
In the input.xml, one to specify the mode=unix to enable the communication via UNIX socket.
<ffsocket mode='unix' name='driver'>
<address>host_address</address>
<port>port</port>
<latency>0.01</latency>
<timeout>5000</timeout>
</ffsocket>
Run I-PI with CP2K on a supercomputer
To run I-PI with CP2K on a supercomputer is also straightforward, one needs to get the hostname where the i-PI is executed, and then replace this variable in the CP2K input files. Here is an example script one can use to run I-PI with CP2K on the Daint machine (CSCS).
HOST=$(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