i-PI: a Universal Force Engine

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.

This is typically a patched version of an electronic structure code, but a simple self-contained Fortran driver that implements Lennard-Jones and Silvera-Goldman potentials is included for test purposes.

Quick Setup and Test

Follow these instructions to set up and test i-PI. It is assumed that i-PI will be run from a Linux environment, with a recent version of Python, Numpy and gfortran, and that the terminal is initially in the i-pi package directory (the directory containing this file).

Source the environment settings file env.sh as $ source env.sh or $ . env.sh. It is useful to put this in your .bashrc or other settings file if you always want to have i-PI available.

Compile the driver code

$ cd drivers
$ make
$ cd ..

Run one of the examples

This will first start the wrapper in the background, redirecting the output to a log file, and then run a couple of instances of the driver code. The progress of the wrapper is followed by monitoring the log file with the tail Linux command.

Optionally, you can make a copy of the directory with the example somewhere else if you want to keep the i-PI directory clean.

$ cd examples/tutorial/tutorial-1/
$ i-pi tutorial-1.xml > log &
$ i-pi-driver -h localhost -p 31415 -m sg -o 15 &
$ i-pi-driver -h localhost -p 31415 -m sg -o 15 &
$ tail -f log

The monitoring can be interrupted with CTRL+C when the run has finished (5000 steps).

Run the automatic test suite

The automatic test suite can be run with the Python package pytest from the root directory of the i-PI project.

$ pytest -v

PEP-8 Compliance

i-PI code should be compliant to a minimal subset of PEP-8 recommendations. Before proceeding to a pull request, or to the merging of a large commit, you can use the following script to automatically prettify the code

` i-pi-pepper -p $IPI_ROOT `