A LAMMPS implementation of volume–temperature replica exchange molecular dynamics

Abstract

A driver module for executing volume–temperature replica exchange molecular dynamics (VTREMD) was developed for the LAMMPS package. As a patch code, the VTREMD module performs classical molecular dynamics (MD) with Monte Carlo (MC) decisions between MD runs. The goal of inserting the MC step was to increase the breadth of sampled configurational space. In this method, states receive better sampling by making temperature or density swaps with their neighboring states. As an accelerated sampling method, VTREMD is particularly useful to explore states at low temperatures, where systems are easily trapped in local potential wells. As functional examples, TIP4P/Ew and TIP4P/2005 water models were analyzed using VTREMD. The phase diagram in this study covered the deeply supercooled regime, and this test served as a suitable demonstration of the usefulness of VTREMD in overcoming the slow dynamics problem. To facilitate using the current code, attention was also paid on how to optimize the exchange efficiency by using grid allocation. VTREMD was useful for studying systems with rough energy landscapes, such as those with numerous local minima or multiple characteristic time scales. Program summaryProgram title: vttemperCatalogue identifier: AEVB_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEVB_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: GNU General Public License, version 3No. of lines in distributed program, including test data, etc.: 49706No. of bytes in distributed program, including test data, etc.: 1249424Distribution format: tar.gzProgramming language: C++/MPI.Computer: Tested on Intel X86 and AMD64 architectures. Should be operational on any computer with a C++ compiler.Operating system: Tested on Linux. Should run on any platform with C++ and MPI library.Has the code been vectorized or parallelized?: Yes. 1 to N processors may be used.RAM: Depends on the system size and how the program is partitioned.Classification: 16.13.External routines: LAMMPS (http://lammps.sandia.gov)Nature of problem: The code implements volume–temperature replica exchange molecular dynamics for LAMMPS. Each replica has its own temperature and density. A two-dimensional temperature–density grid is constructed.Solution method: Extending the ability of the existing temper command in LAMMPS to handle replicas of two state variables.Restrictions: The code is based on LAMMPS. A well-designed grid on temperature and density is required.Running time: Running time depends on the system size and the complexity of the problem. Using 8 processors the test run takes approximately 1 minute.