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)
• Alessandro De Vita (King's College London)
• James Kermode (University of Warwick)
• Lars Pastewka (Fraunhofer IWM)

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.

Copyright 2006-2015.

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

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
• ASE (latest svn trunk recommended)
• Molpro

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

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

   export QUIP_ARCH=linux_x86_64_ifort_icc
   

   You may well need to create your own arch/Makefile.${QUIP_ARCH} file based on an existing file.

2. Ensure that you have sufficiently up-to-date compilers. If you are using GNU compiler suite, you need version 4.4 or later. From Intel, you need version > 11.0.084.

3. 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). Note that the default state is usually with rather heavy debugging on, including bounds checking, which makes the code quite slow.

   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.

4. Compile all modules, libraries and programs with:

   make
   

   From the top-level QUIP directory. All object files and programs are built under build/${QUIP_ARCH}/libquip.a.

   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
   • 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).

5. 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=QUIP_Core/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 simple cubic lattice:

   	1
   	Lattice="4 0 0 0 4 0 0 0 4" Properties=Z:I:1:pos:R:3
   	29 0 0 0 
   

   The Lennard-Jones parameters in the above example is defined in the ip.parms.LJ.xml file under share/Parameters. 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.

6. To compile the Python wrappers (quippy), run

   make quippy
   

   quippy depends on Python and numpy, the Atomic Simulation Environment (ASE) and some features require scipy and/or matscipy.

   More details on the quippy installation process are available in the online documentation.

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

   make test
   

8. 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.