COSMO solvation model: Difference between revisions

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In COSMO the solvent is treated as a continuum with a [[permittivity]] ''ε'', and therefore belongs to the "continuum solvation" group of models. As in all these models COSMO approximates the solvent by a dielectric continuum, surrounding the solute molecules outside of a molecular cavity. The details of the cavity construction differ in different COSMO implementations. 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.

Unlike other continuum solvation models, COSMO derives the polarization charges of the continuum, caused by the polarity of the solute, from a scaled-conductor approximation. If the solvent were an ideal conductor the [[electric potential]] on the cavity surface must disappear. If the distribution of the [[electric charge]] in the molecule is known, e.g. from quantum chemistry, then it is possible to calculate the charge ''q''* on the surface segments. For solvents with finite dielectric constant this charge ''q'' is lower by approximately a factor ''&fnof;''(''&epsilon;''):</ref>{{cite journal |last=A.|first=Klamt|last2=G.|first2=Schüürmann|date=1992|title=COSMO: a new approach to dielectric screening in solvents with explicit expressions for the screening energy and its gradient|url=http://pubs.rsc.org/en/content/articlepdf/1993/p2/p29930000799|journal=J. Chem. Soc.|publisher=Perkin Trans.2|volume=2|issue=5|pages=799-805|doi=10.1039/P29930000799|access-date=25 October 2015}}</ref>

:<math>q = f(\varepsilon) q^*.</math>