Development of New Transferable Coarse-Grained Models of Hydrocarbons

We
have utilized an approach that integrates molecular dynamics
(MD) simulations with particle swarm optimization (PSO) to accelerate
the development of coarse-grained (CG) models of hydrocarbons. Specifically,
we have developed new transferable CG beads, which can be used to
model the hydrocarbons (C5 to C17) and reproduce their experimental
properties with good accuracy. First, the PSO method was used to develop
the CG beads of the decane model represented with a 2:1 (2-2-2-2-2)
mapping scheme. This was followed by the development of the nonane
model described with hybrid 2-2-3-2 and 3:1 (3-3-3) mapping schemes.
The force-field parameters for these three CG models were optimized
to reproduce four experimentally observed properties including density,
enthalpy of vaporization, surface tension, and self-diffusion coefficient
at 300 K. The CG MD simulations conducted with these new CG models
of decane and nonane, at different timesteps, for various system sizes,
and at a range of different temperatures, were able to predict their
density, enthalpy of vaporization, surface tension, self-diffusion
coefficient, expansibility, and isothermal compressibility with good
accuracy. Moreover, a comparison of structural features obtained from
the CG MD simulations and the CG beads of mapped all-atom trajectories
of decane and nonane showed very good agreement. To test the chemical
transferability of these models, we have constructed the models for
hydrocarbons ranging from pentane to heptadecane, by using different
combinations of the CG beads of decane and nonane. The properties
of pentane to heptadecane predicted by these new CG models showed
excellent agreement with the experimental data.