Free-energy Calculations Using Classical Molecular Simulation: Application to the Determination of the Melting Point and Chemical Potential of a Flexible RDX Model.

0461336 - ÚCHP 2017 RIV GB eng J - Journal Article
Sellers, M.S. - Lísal, Martin - Brennan, J.K.
Free-energy Calculations Using Classical Molecular Simulation: Application to the Determination of the Melting Point and Chemical Potential of a Flexible RDX Model.
Physical Chemistry Chemical Physics. Roč. 18, č. 11 (2016), s. 7841-7850. ISSN 1463-9076. E-ISSN 1463-9084
R&D Projects: GA ČR(CZ) GA13-02938S
Grant - others:ARL(US) W911NF-10-2-0039
Institutional support: RVO:67985858
Keywords : solid-liquid coexistence * atomistic simulation * dynamics simulations
Subject RIV: CF - Physical ; Theoretical Chemistry
Impact factor: 4.123, year: 2016

We present an extension of various free-energy methodologies to determine the chemical potential of the solid and liquid phases of a fully-flexible molecule using classical simulation. The methods are applied to the Smith-Bharadwaj atomistic potential representation of cyclotrimethylene trinitramine (RDX), a well-studied energetic material, to accurately determine the solid and liquid phase Gibbs free energies, and the melting point (T-m). We outline an efficient technique to find the absolute chemical potential and melting point of a fully-flexible molecule using one set of simulations to compute the solid absolute chemical potential and one set of simulations to compute the solid-liquid free energy difference. With this combination, only a handful of simulations are needed, whereby the absolute quantities of the chemical potentials are obtained, for use in other property calculations, such as the characterization of crystal polymorphs or the determination of the entropy. Using the LAMMPS molecular simulator, the Frenkel and Ladd and pseudo-supercritical path techniques are adapted to generate 3rd order fits of the solid and liquid chemical potentials. Results yield the thermodynamic melting point T-m = 488.75 K at 1.0 atm. We also validate these calculations and compare this melting point to one obtained from a typical superheated simulation technique.
Permanent Link: http://hdl.handle.net/11104/0260953