QSATS: MPI-driven quantum simulations of atomic solids at zero temperature

Abstract

We describe QSATS, a parallel code for performing variational path integral simulations of the quantum mechanical ground state of monatomic solids. QSATS is designed to treat Boltzmann quantum solids, in which individual atoms are permanently associated with distinguishable crystal lattice sites and undergo large-amplitude zero-point motions around these sites. We demonstrate the capabilities of QSATS by using it to compute the total energy and potential energy of hexagonal close packed solid 4He at the density ρ = 4.61421 × 10 − 3 a 0 − 3 . Program summary Program title: QSATS Catalogue identifier: AEJE_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEJE_v1_0.html Program obtainable from: CPC Program Library, Queenʼs University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 7329 No. of bytes in distributed program, including test data, etc.: 61 685 Distribution format: tar.gz Programming language: Fortran 77. Computer: QSATS should execute on any distributed parallel computing system that has the Message Passing Interface (MPI) [1] libraries installed. Operating system: Unix or Linux. Has the code been vectorized or parallelized?: Yes, parallelized using MPI [1]. RAM: The memory requirements of QSATS depend on both the number of atoms in the crystal and the number of replicas in the variational path integral chain. For parameter sets A and C (described in the long write-up), approximately 4.5 Mbytes and 12 Mbytes, respectively, are required for data storage by QSATS (exclusive of the executable code). Classification: 7.7, 16.13. External routines: Message Passing Interface (MPI) [1] Nature of problem: QSATS simulates the quantum mechanical ground state for a monatomic crystal characterized by large-amplitude zero-point motions of individual (distinguishable) atoms around their nominal lattice sites. Solution method: QSATS employs variational path integral quantum Monte Carlo techniques to project the systemʼs ground state wave function out of a suitably-chosen trial wave function. Restrictions: QSATS neglects quantum statistical effects associated with the exchange of identical particles. As distributed, QSATS assumes that the potential energy function for the crystal is a pairwise additive sum of atom–atom interactions. Additional comments: An auxiliary program, ELOC, is provided that uses the output generated by QSATS to compute both the crystalʼs ground state energy and the expectation value of the crystalʼs potential energy. End users can modify ELOC as needed to compute the expectation value of other coordinate-space observables. Running time: QSATS requires roughly 3 hours to run a simulation using parameter set A on a cluster of 12 Xeon processors with clock speed 2.8 GHz. Roughly 15 hours are needed to run a simulation using parameter set C on the same cluster.