| Abstract
| - An extension of the anisotropic united atoms model is proposed for thiols and sulfides. A complete derivationof the nonbonded parameters is performed with the aim of obtaining a transferable force field. The electrostaticpart of the intermolecular potential is represented by a set of atomic charges. These charges are extractedfrom quantum chemical calculations thanks to a method developed recently. These charges are shown todepend very weakly on the conformation of the molecule. The repulsion−dispersion interactions are describedby an anisotropic united atom Lennard-Jones potential: parameters for methyl and methylene groups aredirectly taken from a previous study on alkanes, whereas parameters for −S and −SH groups are fitted toexperimental data. The resulting potential, which we will term OPPE (optimized potential model for phaseequilibria), is tested against liquid properties at atmospheric pressure and vapor−liquid-phase equilibria ofvarious sulfides and thiols to prove its transferability. Excellent agreement is obtained with experimentaldata.
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