Coarse-grain modelling using an equation-of-state many-body potential: application to fluid mixtures at high temperature and high pressure

ABSTRACT

A many-body, coarse-grain model, termed the product gas mixture model, is presented that accurately describes the thermodynamic behaviour of molecular mixtures. The coarse-grain model is developed by first approximating the mixture as a van der Waals one-fluid, and subsequently applying an exponential-6 equation-of-state to describe the forces and energies between particles in the spirit of the many-body model pioneered by Pagonabarraga and Frenkel. Isothermal dissipative particle dynamics simulations are carried out at thermochemical states that occur during decomposition of a prototypical energetic material, RDX (1,3,5-trinitro-1,3,5-triazinane). The product gas mixture model performance is assessed by comparing to an explicit-molecule model and a hard-core coarse-grain model based on the exponential-6 pair potential. Overall, the many-body, coarse-grain model is shown to accurately capture the structural and thermodynamic properties for the wide variety of thermochemical states considered, while the hard-core coarse-grain model cannot. The many-body, coarse-grain model overcomes the issues of transferability, scaling consistency and unphysical ordered phase behaviour that often afflict coarse-grain models. While specific thermochemical conditions related to RDX decomposition are considered, the results are generally applicable to the thermodynamic behaviour of other fluid mixtures at both moderate and extreme conditions.

GRAPHICAL ABSTRACT

KEYWORDS:

• Coarse-grain model
• dissipative particle dynamics
• many-body potential
• product gas mixture
• exponential-6 potential

Acknowledgments

The authors wish to acknowledge insightful discussions with Michael Sellers (Bryan Research and Engineering; previously the Army Research Laboratory (ARL)), Gabriel Stoltz (École des Ponts ParisTech), Michael E. Fortunato (University of Florida), Patrick G. Lafond and Sergei Izvekov (ARL). J. Matthew Mansell acknowledges the support from the Department of Defense (DoD) High Performance Computing Modernization Program (HPCMP) Internship Program [project number HIP-17-015]. Martin Lísal acknowledges the support from the Army Research Office (project No. W911NF-16-1-0566) and the Czech Science Foundation (project No. 16-12291S). James P. Larentzos and John K. Brennan acknowledge the support from the Office of Naval Research (Advanced Energetic Materials programme). This work was supported in part by a grant of computer time from the DoD HPCMP at the ARL DoD Supercomputing Resource Centre (ARL DSRC).

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. The nomenclature found in the literature, many-body dissipative particle dynamics (MDPD), can be misleading. Strictly, ‘MDPD’ refers to a particular type of conservative force, i.e. local density-dependent forces as opposed to a unique DPD variant or set of equations-of-motion. Nothing precludes the implementation of an ‘MDPD model’ in a method other than DPD, such as molecular dynamics or Monte Carlo. As such, the nomenclature ‘CG many-body potential’ is used throughout this work.

Additional information

Funding

Department of Defense (DoD) High Performance Computing Modernization Program (HPCMP) Internship Program [project number HIP-17-015]; Army Research Office [project no. W911NF-16-1-0566]; Czech Science Foundation [project no. 16-12291S]; Office of Naval Research (Advanced Energetic Materials programme) [project number N0001417MP00163].