Trial structures generated by USPEX are relaxed and then evaluated by an external code interfaced with USPEX. Based on the obtained ranking of relaxed structures, USPEX generates new structures — which are again relaxed and ranked. Our philosophy is to use existing well-established ab initio (or classical forcefield) codes for structure relaxation and energy calculations. Currently, USPEX is interfaced with:
VASP — https://www.vasp.at/
LAMMPS — http://lammps.sandia.gov/
DMACRYS — http://www.chem.ucl.ac.uk/basictechorg/dmacrys/index.html
CP2K — http://www.cp2k.org/
Quantum Espresso — http://www.quantum-espresso.org/
FHI-aims — https://aimsclub.fhi-berlin.mpg.de/
ATK — http://quantumwise.com/
CASTEP — http://www.castep.org/
Tinker — http://dasher.wustl.edu/tinker/
MOPAC — http://openmopac.net/
Gaussian — http://www.gaussian.com/index.htm
ORCA — https://orcaforum.cec.mpg.de
DFTB — http://www.dftb-plus.info
We chose these codes based on 1) their efficiency for structure relaxation; 2) robustness; and 3) popularity. Of course, there are other codes that can satisfy these criteria, and in the future we can interface USPEX to them.