Transferability and nonbond functional form of coarse grained force field - tested on linear alkanes.

Whether or not a coarse grained force field (CGFF) can be made to be transferrable is an important question to be addressed. By comparing potential energy with potential of mean force (PMF) of a molecular dimer, we proposed to use a free energy function (FE-12-6) with the parameters in entropic and energetic terms explicitly to represent the nonbond interactions in CGFF. Although the FE-12-6 function cannot accurately describe the PMF curves, a cancelation of short radii and strong repulsion makes the function a good approximation. For nonpolar molecules represented by linear alkanes, FE-12-6 is demonstrated to be highly effective in representing the nonbond interactions in CGFF. The force field parameters are well transferrable among different alkane molecules, in different thermodynamic states and for predicting various thermodynamic properties including heats of vaporization, vapor-liquid-equilibrium coexistence curves, surface tensions, and liquid densities.