AB-INITIO CALCULATION OF MOLAR VOLUMES - COMPARISON WITH EXPERIMENT AND USE IN SOLVATION MODELS

A simple and efficient procedure of calculating molecular volume (V-M) based on the Monte Carlo method is presented. The volume of a molecul e is defined by the volume occupied by the 0.001-au electron density e nvelope. We have employed this method to compute the molecular volumes (V-M) of a large selection of organic molecules and compare them with the corresponding molar volumes (V-m) measured in the liquid state. A strong correlation is found to exist between the V-M and V-m values ( V-M/V-m approximate to 0.75). Using this linear relationship, the calc ulated molecular volume may provide an estimate of the cavity-volume p arameter in solvent-effect calculations. As a chemical application of molecular volume, we have investigated the conformational equilibrium of 1,2-difluoroethane in the liquid state using the self-consistent re action field theory. (C) 1995 by John Wiley & Sons, Inc.