In this work, we provide an interface developed to link the Molecular Modelling toolkit (MMTK) with OpenMM in order to take advantage of the fast evaluation techniques of OpenMM. This interface allows MMTK scripts using the Langevin dynamics integrator, for both classical and path integral simulations, to be executed on a variety of hardware including graphical processing units via OpenMM. The interface has been developed using Python and Cython to take advantage of the high level abstraction thanks to the MMTK and OpenMM software packages. We have tested the interface on a number of systems to observe which systems benefit most from the acceleration libraries of OpenMM.Program summaryProgram title: OpenMM accelerated MMTKCatalogue identifier: AEVR_v1_0Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEVR_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 1141No. of bytes in distributed program, including test data, etc.: 101838Distribution format: tar.gzProgramming language: Python and Cython.Computer: Not computer specific.Operating system: Any.RAM: On the order of hundreds of MBytesClassification: 7.7.External routines: MMTK [1], OpenMM 6.1 [2] and their dependenciesNature of problem: The OpenMM accelerated MMTK interface provides MMTK users the full performance of OpenMM simulations while maintaining the flexibility of MMTK.Solution method: The interface has been developed in a combination of Python and Cython to take advantage of the high level Python API's of both OpenMM and MMTK. The interface provides OpenMM with the required information to perform simulations and MMTK stores the relevant information.Unusual features: Provides MMTK users a performance gain with hardly any modifications to their current scripts.Running time: Completely depends on system of interest. Running time is based on both the number of atoms in the simulation as well as the number of path integral beads used in simulation and ranges from a few seconds to months.References:[1] K. Hinsen, J. Comp. Chem. 21, 79, (2000).[2] P. Eastman et al., J. Chem. Theory Comput. 9, 461 (2013). (C) 2015 Elsevier B.V. All rights reserved.

We developed and studied the implementation of trial wavefunctions in the newly proposed Langevin equation Path Integral Ground State (LePIGS) method [S. Constable, M. Schmidt, C. Ing, T. Zeng, and P.-N. Roy, J. Phys. Chem. A 117, 7461 (2013)]. The LePIGS method is based on the Path Integral Ground State (PIGS) formalism combined with Path Integral Molecular Dynamics sampling using a Langevin equation based sampling of the canonical distribution. This LePIGS method originally incorporated a trivial trial wavefunction, ψT, equal to unity. The present paper assesses the effectiveness of three different trial wavefunctions on three isotopes of hydrogen for cluster sizes N = 4, 8, and 13. The trial wavefunctions of interest are the unity trial wavefunction used in the original LePIGS work, a Jastrow trial wavefunction that includes correlations due to hard-core repulsions, and a normal mode trial wavefunction that includes information on the equilibrium geometry. Based on this analysis, we opt for the Jastrow wavefunction to calculate energetic and structural properties for parahydrogen, orthodeuterium, and paratritium clusters of size N = 4 − 19, 33. Energetic and structural properties are obtained and compared to earlier work based on Monte Carlo PIGS simulations to study the accuracy of the proposed approach. The new results for paratritium clusters will serve as benchmark for future studies. This paper provides a detailed, yet general method for optimizing the necessary parameters required for the study of the ground state of a large variety of systems.

We propose a Langevin equation path integral ground state (LePIGS) approach for the calculation of ground state (zero temperature) properties of molecular systems. The approach is based on a modification of the finite temperature path integral Langevin equation (PILE) method (J. Chem. Phys. 2010, 133, 124104) to the case of open Feynman paths. Such open paths are necessary for a ground state formulation. We illustrate the applicability of the method using model systems and the weakly bound water-parahydrogen dimer. We show that the method can lead to converged zero point energies and structural properties.

Author Institution: Department of Chemistry, University of Waterloo, Waterloo, ON, Canada, N2L 3G1; Department of Biochemistry, University of Toronto, 27 King's College Circle, Toronto, Ontario, Canada M5S 1A1; Department of Chemistry, University of Waterloo, Waterloo, ON, Canada, N2L 3G1