Refinement and Parametrization of COSMO-RS

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., ∆G 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.

Interpretation of experimental hydrogen-bond enthalpies and entropies from COSMO polarisation charge densities

“…Indeed, this is in quite good agreement with the fact that the polarisation charge densities in a non-polar solvent typically are by a factor of 0.8 smaller than in a conductor, due to the almost complete lack of electronic back-polarisation in non-polar solvents. 36 Since we are using as descriptors s values calculated in a conductor environment here, and since this reduction applies to the donor and acceptor, we would expect a reduction of the slope of DH o HB , vs. s by a factor of B0.8 2 = 64%.…”

“…The suitability of the polarisation charge density for the quantification of intermolecular interaction has been demonstrated by Klamt in his COSMO-RS solvation model. [20][21][22] For those not familiar with the concept of COSMO, a more detailed description and discussion of the polarisation charge density s is given in appendix SI1 in the ESI. † The study on the quantum chemically calculated HB complexes confirmed the bilinear s-dependence of HB bond energies assumed within the COSMO-RS.…”

Free-energy perturbation and quantum mechanical study of SAMPL4 octa-acid host–guest binding energies

“…These calculations were performed with default values for all parameters (implying a water-like probe molecule) and a dielectric constant of 80. For the generation of the cavity, we used the optimised COSMO radii in Turbomole (1.30, 2.00, 1.72, and 2.05 Å for H, C, O, and Cl, respectively) [59].…”

Assessing the reliability of predictive activity coefficient models for molecules consisting of several functional groups

“…The total number of surface segments in a molecule is i i e f f n A a = , where 2 eff a a r ν = π is the standard segment surface area and av r is the averaging radius, one of the adjustable parameters studied in this paper. It is usual in the literature to find two values for the averaging radius (Grensemann & Gmehling, 2005;Klamt et al, 1998), one used to determine the surface area eff (r ) and another for the σ-profile averaging procedure av (r ) . In this work, av r will be used in both calculations.…”