Evaluating the Ability of Selected Force Fields to Simulate Hydrocarbons as a Function of Temperature and Pressure Using Molecular Dynamics
Brian H. Morrow, Judith A. Harrison
Abstract
The ability of both nonreactive (OPLS-AA) and reactive (AIREBO-M and ReaxFF) force fields to model pure hydrocarbon fluids at various temperatures and pressures was assessed using molecular dynamics. Four molecules, trans-decalin, n-hexadecane, isocetane, and tetralin, were chosen, representing cyclic, linear, branched, and aromatic hydrocarbons, respectively. Temperatures ranged from 293.15 to 373.15 K at 0.1 MPa, and pressures ranged from 0.1 to 40 MPa at 313.15 K. The OPLS-AA force field was the most accurate in predicting densities, while ReaxFF gave slightly better isentropic bulk modulus predictions. For both properties, the AIREBO-M potential was much less accurate than the other two potentials. The fluid structure was quantified using radial distribution functions and angular radial distribution functions. Tetralin molecules were found to have a much higher propensity for parallel arrangements in the simulations using AIREBO-M and ReaxFF than those that used OPLS-AA. For all other molecules, the three force fields gave qualitatively similar fluid structures. When utilizing the ReaxFF potential, radius of gyration histograms show that n-hexadecane molecules have a higher probability of sampling bent conformations than they do in the AIREBO-M and OPLS-AA simulations, where the molecules tend to be more fully extended.