Derivation of an optimized potential model for phase equilibria (OPPE) forsulfides and thiols

An extension of the anisotropic united atoms model is proposed for thiols a nd sulfides. A complete derivation of the nonbonded parameters is performed with the aim of obtaining a transferable force field. The electrostatic pa rr of the intermolecular potential is represented by a set of atomic charge s. These charges are extracted from quantum chemical calculations thanks to a method developed recently. These charges are shown to depend very weakly on the conformation of the molecule. The repulsion-dispersion interactions are described by an anisotropic united atom Lennard-Jones potential: param eters for methyl and methylene groups are directly taken from a previous st udy on alkanes, whereas parameters for -S and -SH groups are fitted to expe rimental data. The resulting potential, which we will term OPPE (optimized potential model for phase equilibria), is tested against liquid properties at atmospheric pressure and vapor-liquid-phase equilibria of various sulfid es and thiols to prove its transferability. Excellent agreement is obtained with experimental data.