An improved united-atom potential for molecular dynamics simulation of saturated properties of n-alkanes

Multiple united-atom (UA) potential models have been developed in the literature to reproduce experimental saturated properties of n-alkanes using Monte Carlo simulations. When these UA potentials are employed in molecular dynamics (MD) simulations, MD simulations often give relatively poor predictions of saturated properties of n-alkanes, particularly the saturated vapor densities, due to the challenges in accurate calculation of long-range intermolecular forces beyond the cutoff distance in an inhomogeneous system. In this work, a new set of UA Lennard-Jones (LJ) interaction parameters for n-alkanes is proposed to reproduce the saturated properties, including saturated liquid and vapor densities (ρf and ρg); saturated vapor pressure (Psat); critical temperature, density, and pressure (Tcr, ρcr, and Pcr); surface tension (γ); latent heat of vaporization (hfg); and saturated liquid viscosity (η) of n-alkanes (C4-C22) using MD simulations with truncated LJ interactions. Compared to the experimental data of n-alkanes properties, the average absolute deviation of the MD simulation results obtained using the improved UA (I-UA) potential developed in this work are 1.6%, 2.3%, 2.8%, 0.3%, 2.7%, 4.3%, 4.4%, 2.1%, and 14.3% for ρf, ρg, Psat, Tcr, ρcr, Pcr, γ, hfg, and η, respectively. The Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code for MD simulation of liquid-vapor equilibrium of n-dodecane using the I-UA potential is provided in this paper. The LAMMPS code can be easily modified to determine saturated properties of other n-alkanes.