REFINEMENT AND PARAMETRIZATION OF COSMO-RS

The continuum solvation model COSMO and its extension beyond the diele ctric approximation (COSMO RS) have been carefully parametrized in ord er to optimally reproduce 642 data points for a variety of properties, i.e., Delta G of hydration, vapor pressure, and the partition coeffic ients for octanol/water, benzene/water, hexane/ water, and diethyl eth er/water. Two hundred seventeen small to medium sized neutral molecule s, covering most of the chemical functionality of the elements H, C, N , O, and Cl, have been considered. An overall accuracy of 0.4 (rms) kc al/mol for chemical potential differences, corresponding to a factor o f 2 in the equilibrium constants under consideration, has been achieve d. This was using only a single radius and one dispersion constant per element and a total number of eight COSMO-RS inherent parameters. Mos t of these parameters were close to their theoretical estimate. The op timized cavity radii agreed well with the widely accepted rule of 120% of van der Weals radii. The whole parametrization was based upon dens ity functional calculations using DMol/COSMO. As a result of this soun d parametrization, we are now able to calculate almost any chemical eq uilibrium in liquid/liquid and vapor/liquid systems up to an accuracy of a factor 2 without the need of any additional experimental data for solutes or solvents. This opens a wide range of applications in physi cal chemistry and chemical engineering.