Refinement and Parametrization of COSMO-RS

TLDR

COSMO‑RS is a continuum solvation model that has been parametrized to reproduce 642 data points for properties such as hydration free energies, vapor pressures, and partition coefficients across several solvent systems. The authors parametrized COSMO‑RS using density‑functional calculations on 217 neutral molecules, employing a single radius and one dispersion constant per element and eight inherent parameters. The parametrization achieves an overall 0.4 kcal mol⁻¹ rms accuracy (≈factor 2 in equilibrium constants), with parameters near theoretical values and cavity radii matching the 120 % van der Waals rule, enabling accurate prediction of liquid/liquid and vapor/liquid equilibria without extra experimental data and opening broad applications in physical chemistry and chemical engineering.

Abstract

The continuum solvation model COSMO and its extension beyond the dielectric approximation (COSMO-RS) have been carefully parametrized in order to optimally reproduce 642 data points for a variety of properties, i.e., ΔG of hydration, vapor pressure, and the partition coefficients for octanol/water, benzene/water, hexane/water, and diethyl ether/water. Two hundred seventeen small to medium sized neutral molecules, 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) kcal/mol for chemical potential differences, corresponding to a factor of 2 in the equilibrium constants under consideration, has been achieved. This was using only a single radius and one dispersion constant per element and a total number of eight COSMO-RS inherent parameters. Most of these parameters were close to their theoretical estimate. The optimized cavity radii agreed well with the widely accepted rule of 120% of van der Waals radii. The whole parametrization was based upon density functional calculations using DMol/COSMO. As a result of this sound parametrization, we are now able to calculate almost any chemical equilibrium 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 physical chemistry and chemical engineering.