An Optimized Force Field for Vapor-Liquid Equilibria and Molecular Dynamics Simulations of Eco-Friendly Dielectric Fluid Perfluoronitriles.

A classical all-atom force field for perfluoronitriles (PFN-AA) is proposed for simulating the phase equilibria and dynamic transport properties of perfluoronitrile compounds that are a promising chemical family as a novel eco-friendly replacement for SF6 in various applications. The force-field parameters are developed primarily by fitting to molecular structures, vibrational frequencies, energetic profiles of the conformational rotation, and intermolecular interactions of the dimeric complexes from ab initio calculations. The performance of the PFN-AA force field is examined by simulating the vapor-liquid coexistence and physical properties of heptafluoro-iso-butyronitrile (C4) using the Gibbs ensemble simulation with the hybrid configurational-bias Monte Carlo technique and the molecular dynamics simulations. Theoretical vapor pressures and the boiling point of the pure C4 compound are in excellent agreement with available experimental data. The physical properties of C4 in the phase envelope including critical properties, self-diffusion coefficients, dielectric constants, shear viscosity, thermal conductivity, and thermodynamic properties are predicted computationally for the first time. In addition, the transferability of the PFN-AA force field with respect to other force fields, i.e., EPM2 for CO2, is validated by the successful description of the fluoronitrile/CO2 mixture. The current PFN-AA force field outperforms the generic potential models (e.g., COMPASS and CVFF) in the understanding of the fundamental properties of the novel perfluoronitrile dielectric fluids and their mixtures.