Parametrization of 2-Bromo-2-Chloro-1,1,1-Trifluoroethane (Halothane) and Hexafluoroethane for Nonbonded Interactions

Abstract

Ab initio and empirical methods were combined to optimize the partial atomic charges and Lennard-Jones parameters for two halogenated compounds, halothane (CF3CHClBr, a potent volatile anesthetic) and hexafluoroethane (CF3CF3, a nonanesthetic). Charge optimization was achieved using empirical calculations by systematically adjusting the charge assignments to fit minimum interaction energies and geometries between a TIP3 water molecule and the halogenated compounds to the corresponding values from the ab initio calculations, which were carried out at the HF/6-311+G(2d,p) and HF/6-31G(d) levels for halothane and hexafluoroethane, respectively. To optimize the Lennard-Jones parameters, the initial estimates were obtained from scaling the values from the ab initio minimum interaction energies and geometries between neon and the halogenated compounds calculated at the MP3/6-311++G(3d,3p) level. The Lennard-Jones parameters were further refined by fitting the empirical interaction energies to the corresponding ...