# libAtoms/QUIP

libAtoms/QUIP molecular dynamics framework: http://www.libatoms.org
Fortran Python C Shell TeX Makefile Other
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# QUIP - QUantum mechanics and Interatomic Potentials

The QUIP package is a collection of software tools to carry out molecular dynamics simulations. It implements a variety of interatomic potentials and tight binding quantum mechanics, and is also able to call external packages, and serve as plugins to other software such as LAMMPS, CP2K and also the python framework ASE. Various hybrid combinations are also supported in the style of QM/MM, with a particular focus on materials systems such as metals and semiconductors.

For more details, see the online documentation.

Long term support of the package is ensured by:

• Noam Bernstein (Naval Research Laboratory)
• Gabor Csanyi (University of Cambridge)
• James Kermode (University of Warwick)

Portions of this code were written by: Albert Bartok-Partay, Livia Bartok-Partay, Federico Bianchini, Anke Butenuth, Marco Caccin, Silvia Cereda, Gabor Csanyi, Alessio Comisso, Tom Daff, ST John, Chiara Gattinoni, Gianpietro Moras, James Kermode, Letif Mones, Alan Nichol, David Packwood, Lars Pastewka, Giovanni Peralta, Ivan Solt, Oliver Strickson, Wojciech Szlachta, Csilla Varnai, Steven Winfield.

Most of the publicly available version is released under the GNU General Public license, version 2, with some portions in the public domain.

## Features

The following interatomic potentials are presently coded or linked in QUIP:

• BKS (van Beest, Kremer and van Santen) (silica)
• EAM (fcc metals)
• Fanourgakis-Xantheas (water)
• Finnis-Sinclair (bcc metals)
• Flikkema-Bromley
• GAP (Gaussian Approximation Potentials: general many-body)
• Guggenheim-!McGlashan
• Brenner (carbon)
• OpenKIM (general interface)
• Lennard-Jones
• Morse
• Partridge-Schwenke (water monomer)
• Stillinger-Weber (carbon, silicon, germanium)
• SiMEAM (silicon)
• Sutton-Chen
• Tangney-Scandolo (silica, titania etc)
• Tersoff (silicon, carbon)

The following tight-binding functional forms and parametrisations are implemented:

• Bowler
• DFTB
• GSP
• NRL-TB

The following external packages can be called:

• CASTEP
• VASP
• CP2K
• ASAP
• Molpro
• ASE (required if using quippy Python interface; latest version recommended)

## Code philosophy and goals

QUIP was born because of the need to efficiently tie together a wide variety of different models, both empirical and quantum mechanical. It will not be competitive in terms of performance with codes such as LAMMPS and Gromacs, but has a number of unique features:

• Deep access to most of the Fortran types and routines from Python via the quippy package
• Support for Gaussian Approximation Potentials (GAP)
• Does not assume minimum image convention, so interatomic potentials can have cutoffs that are larger than the unit cell size

## Compilation Instructions

1. To compile QUIP the minimum requirements are:

• A working Fortran compiler. QUIP is tested with gfortran 4.4 and later, and ifort 11.1.

• Linear algebra libraries BLAS and LAPACK. QUIP is tested with reference versions libblas-dev and liblapack-dev on Ubuntu 12.04, and mkl 11.1 with ifort.

2. Clone the QUIP repository from GitHub. The --recursive option brings in submodules automatically (If you don't do this, then you will need to run git submodule update --init from the top-level QUIP directory after cloning) ::

git clone --recursive https://github.com/libAtoms/QUIP.git

3. Decide your architecture by looking in the arch/ directory, and define an environmental variable QUIP_ARCH, e.g.::

export QUIP_ARCH=linux_x86_64_gfortran


for standard gfortran on Linux. You may need to create your own arch/Makefile.${QUIP_ARCH} file based on an existing file for more exotic systems. 4. Customise QUIP, set the maths libraries and provide linking options:: make config  Makefile.config will create a build directory, build/${QUIP_ARCH}, and all the building happen there. First it will ask you some questions about where you keep libraries and other stuff, if you don't use something it is asking for, just leave it blank. The answers will be stored in Makefile.inc in the build/${QUIP_ARCH} directory, and you can edit them later (e.g. to change optimisation or debug options). If you later make significant changes to the configuration such as enabling or disabling tight-binding support you should force a full rebuild by doing a make deepclean; make. 5. Compile all programs, modules and libraries:: make  From the top-level QUIP directory. All programs are built in build/${QUIP_ARCH}/. You can also find compiled object files and libraries (libquip.a) in that directory. Programs can be called directly from that directory.

Other useful make targets include:

• make install : copies all compiled programs it can find to QUIP_INSTALLDIR, if it's defined and is a directory (full path required), and copies bundled structures to QUIP_STRUCTS_DIR if it is defined.

• make libquip: Compile QUIP as a library and link to it. This will make all the various libraries and combine them into one: build/${QUIP_ARCH}/libquip.a, which is what you need to link with (as well as LAPACK). 6. A good starting point is to use the quip program, which can calculate the properties of an atomic configuration using a variety of models. For example:: quip at_file=test.xyz init_args='IP LJ' \ param_file=share/Parameters/ip.parms.LJ.xml E  assuming that you have a file called test.xyz with the following data in it representing Cu atoms in a cubic fcc lattice:: 4 Lattice="3.61 0 0 0 3.61 0 0 0 3.61" Properties=species:S:1:pos:R:3 Cu 0.000 0.000 0.000 Cu 0.000 1.805 1.805 Cu 1.805 0.000 1.805 Cu 1.805 1.805 0.000  The Lennard-Jones parameters in the above example are defined in the ip.parms.LJ.xml file under share/Parameters (ensure the path to this file is correct). The format of the atomic configuration is given in Extended XYZ format, in which the first line is the number of atoms, the second line is a series of key=value pairs, which must at least contain the Lattice key giving the periodic bounding box and the Properties key that describes the remaining lines. The value of Properties is a sequence of triplets separated by a colon (:), that give the name, type and number of columns, with the type given by I for integers, R for reals, S for strings. Most string arguments can be replaced by --help and QUIP programs will then print a list of allowable keywords with brief help messages as to their usage, so e.g. init_args=--help will give a list of potential model types (and some combinations). The parsing is recursive, so init_args="IP --help" will then proceed to list the types of interatomic potentials (IP) that are available. 7. To compile the Python wrappers (quippy), the minimum requirements are: 8. If you are using a Python virtual environment (virtualenv) and would like to install quippy into it, ensure the environment is activated (source <env_dir>/bin/activate, where <env_dir> is the root of your virtual environment) before building quippy (otherwise library versions may cause unexpected conflicts). 9. To compile the Python wrappers (quippy), run:: make quippy  Quippy can be used by adding the lib directory in quippy/build/${QUIP_ARCH} to your $PYTHONPATH, however it can be more convenient to install into a specific Python distribution:: make install-quippy  will either install into the current virtualenv or attempt to install systemwide (usually fails without sudo). To install only for the current user (into ~\.local), execute the command QUIPPY_INSTALL_OPTS=--user make install-quippy, or use QUIPPY_INSTALL_OPTS=--prefix=<directory> to install into a specific directory. QUIPPY_INSTALL_OPTS can also be set in the file build/${QUIP_ARCH}/Makefile.inc.

10. More details on the quippy installation process and troubleshooting for common build problems are available in the online documentation.

11. To run the unit and regression tests, which depend on quippy::

make test

12. Some functionality is only available if you check out other modules within the QUIP/src/ directories, e.g. the ThirdParty (DFTB parameters, TTM3f water model), GAP (Gaussian Approximation Potential models) and GAP-filler (Gaussian Approximation Potential model training). These packages are not distributed with QUIP because they come with different licensing restrictions.

13. In order to run QUIP potentials via LAMMPS, make libquip to get QUIP into library form, and then follow the instructions in the LAMMPS documentation.