COSMO solvation model

COSMO[1][2] (COnductor-like Screening MOdel) is a calculation method for determining the electrostatic interaction of a molecule with a solvent.

In most cases it is constructed as an assembly of atom-centered spheres with radii approximately 20% larger than the Van der Waals radius.

For the actual calculation the cavity surface is approximated by segments, e.g., hexagons, pentagons, or triangles.

If the solvent were an ideal conductor the electric potential on the cavity surface must disappear.

[1] COSMO has been implemented in a number of quantum chemistry or semi-empirical codes such as ADF, GAMESS-US, Gaussian, MOPAC, NWChem, TURBOMOLE, and Q-Chem.

A COSMO version of the polarizable continuum model PCM has also been developed [citation needed].

Depending on the implementation, the details of the cavity construction and the used radii, the segments representing the molecule surface and the

While models based on the multipole expansion of the charge distribution of a molecule are limited to small, quasi-spherical or ellipsoidal molecules, the COSMO method has the advantage (as many other dielectric continuum models) that it can be applied to large and irregularly formed molecular structures.

In contrast to the polarizable continuum model (PCM), which uses the exact dielectric boundary conditions, the COSMO method uses the approximative scaling function

A method comparison[7] of COSMO and the integral equation formalism PCM (IEFPCM), which combines the exact dielectric boundary conditions with a reduced outlying charge error, showed that the differences between the methods are small as compared to deviations to experimental solvation data.

The errors introduced by treating a solvent as a continuum and thus neglecting effects like hydrogen bonding or reorientation are thus more relevant to reproduce experimental data than the details of the different continuum solvation methods.