QUIP library

Albert Bartok-Partay apbartok at gmail dot com 2014

This library provides a plug-in for calling QUIP potentials from LAMMPS. The QUIP package should be built separately, and then the resulting libraries can be linked to the LAMMPS code. In case of some potentials, such as BOP or GAP, third-party packages are needed, which must be downloaded and compiled separately. NB: although GAP has to be downloaded separately as it is licensed under a different license agreement, it is compiled together with the rest of QUIP.

Building LAMMPS with QUIP support:

1. Building QUIP

1.1) Obtaining QUIP

The most current release of QUIP can be obtained from github:

$ git clone https://github.com/libAtoms/QUIP.git QUIP

If GAP is needed, it may be downloaded from the `Software' section of libatoms.org, after accepting the terms and conditions of the Academic License Agreement. Extract the tarball under the /path/to/QUIP/src/ directory.

1.2) Building QUIP

There is a README file in the top-level QUIP directory, but here are the main steps.

The arch directory contains a selection of machine- and compiler-specific makefiles, e.g. Makefile.linux_x86_64_gfortran. Decide which one is most appropriate for your system, and edit if necessary. The configuring step will use the makefile based on the QUIP_ARCH environment variable, i.e. Makefile.${QUIP_ARCH}. The script will create a build directory, build/${QUIP_ARCH}, and all the building will happen there. First it will ask you some questions about where you keep libraries and other stuff.

Please note: if you are building QUIP to link it to LAMMPS, the serial version of QUIP must be compiled. For example, QUIP_ARCH may be: darwin_x86_64_gfortran linux_x86_64_gfortran linux_x86_64_ifort_icc etc.

If you don't use something it is asking for, just leave it blank. NB make sure to answer y' to Do you want to compile with GAP prediction support ? [y/n]'. The answers will be stored in Makefile.inc in the build/${QUIP_ARCH} directory, and you can edit them later (e.g. to change optimisation or debug options). Note that the default state is usually with rather heavy debugging on, including bounds checking, which makes the code quite slow. The make command has to be executed from the top-level directory. Making `libquip' ensures all the necessary libraries will be built.

for example:

$ cd QUIP $ export QUIP_ROOT=${PWD} $ export QUIP_ARCH=linux_x86_64_gfortran $ make config $ make libquip

Optionally, do $ make test to run a test suite.

2. Building LAMMPS

Edit Makefile.lammps in the lib/quip folder, if necessary. If you have cloned, configured, and built QUIP inside this folder, QUIP_ROOT and QUIP_ARCH should be autodetected, even without having to set the environment variables. Otherwise export the environment variables as shown above or edit Makefile.lammps

LAMMPS ships with a user package containing the interface necessary to use QUIP potentials, but it needs to be added to the compilation first. To do that, enter the LAMMPS source directory and type:

$ make yes-user-quip

2.2) Build LAMMPS according to the instructions on the LAMMPS website.

3. There are three example sets in examples/USER/quip:

• a set of input files to compute the energy of an 8-atom cubic diamond cell of silicon with the Stillinger-Weber potential. Use this to benchmark that the interface is working correctly.

• a set of input files demonstrating the use of the QUIP pair style for a molecular system with pair style hybrid/overlay and different exclusion settings for different pair styles. This input is for DEMONSTRATION purposes only, and does not simulate a physically meaningful system.

• a set of input files to demonstrate how GAP potentials are specified in a LAMMPS input file to run a short MD. The GAP parameter file gap_example.xml is intended for TESTING purposes only. Potentials can be downloaded from http://www.libatoms.org or obtained from the authors of QUIP.