Program summary:
Program title: TTCF4LAMMPS
CPC Library link to program files: https://doi.org/10.17632/hh2rkcxbrf.1
Developer's repository link: https://github.com/edwardsmith999/TTCF4LAMMPS
Licensing provisions: GNU General Public License 3
Programming language: Python 3
Nature of problem: Measuring the nonequilibrium behaviour of bulk and confined fluids under experimentally accessible strain rates in non-equilibrium molecular dynamics (NEMD) simulations.
Solution method: Creating a Python-based code that utilises the transient-time correlation function method and the LAMMPS software to enable the bulk fluid properties (e.g. viscosity) and confined fluid interfacial properties (e.g. shear stress and slip velocity) to be computed at low shear rates with NEMD.Data availability:
All data used in this work are freely reproducible using the program provided. The source files are also available at the link https://github.com/edwardsmith999/TTCF4LAMMPS.We present TTCF4LAMMPS, a toolkit for performing non-equilibrium molecular dynamics (NEMD) simulations to study the fluid behaviour at low shear rates using the LAMMPS software. By combining direct NEMD simulations and the transient-time correlation function (TTCF) technique, we study the fluid response to shear rates spanning 15 orders of magnitude. We present two examples for simple monatomic systems: one consisting of a bulk liquid and another with a liquid layer confined between two solid walls. The small bulk system is suitable for testing on personal computers, while the larger confined system requires high-performance computing (HPC) resources. We demonstrate that the TTCF formalism can successfully detect the system response for arbitrarily weak external fields. We provide a brief mathematical explanation for this feature. Although we showcase the method for simple monatomic systems, TTCF can be readily extended to study more complex molecular fluids. Moreover, in addition to shear flows, the method can be extended to investigate elongational or mixed flows as well as thermal or electric fields. The high computational cost needed for the method is offset by the two following benefits: i) the cost is independent of the magnitude of the external field, and ii) the simulations can be made highly efficient on HPC architectures by exploiting the parallel design of the algorithm. We expect the toolkit to be useful for computational researchers striving to study the nonequilibrium behaviour of fluids under experimentally-accessible conditions.We thank the Australian Research Council for a grant obtained through the Discovery Projects Scheme (Grant No. DP200100422) and The Royal Society for support via International Exchanges, Grant No. IES/R3/170/233. J.P.E. was supported by the Royal Academy of Engineering (RAEng) through their Research Fellowships scheme. D.D. was supported through a Shell/RAEng Research Chair in Complex Engineering Interfaces. The authors acknowledge the Swinburne OzSTAR Supercomputing facility and the Imperial College London Research Computing Service (DOI:https://doi.org/10.14469/hpc/2232) for providing computational resources for this work. We thank Debra Bernhardt and Stephen Sanderson (University of Queensland) for useful discussions regarding the implementation of SLLOD in LAMMPS
