COSMO solvation model: Difference between revisions

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{{Short description|Computational model for solvent effects}}

[[Image:Pentaacrylat.png|thumb|COSMO surface of a pentaacrylate molecule (red = negative, green = positive equilibrium layer).]]

[[File:4-Nitrobenzoic-acid-elpot-3D-vdW.png|thumb|Charge density surface of 4-nitro-benzoicacid. Calculated with COSMO.]]

'''COSMO'''<ref name=":0" /><ref name=":1" /> (COnductor-like Screening MOdel) is a calculation method for determining the [[electrostatic]] interaction of a [[molecule]] with a [[solvent]]. COSMO is a dielectric continuum model<ref name=":0" /><ref name=":3">{{Cite journal |last=Herbert |first=John M. |date=2021-03-23 |title=Dielectric continuum methods for quantum chemistry |journal=WIREs Computational Molecular Science |volume=11 |issue=4 |doi=10.1002/wcms.1519 |arxiv=2203.06846 |s2cid=233629977 |issn=1759-0876}}</ref><ref>{{Cite book |last=Cramer |first=Christopher J. |title=Essentials of computational chemistry: theories and models |date=2004 |publisher=Wiley |isbn=0-470-09182-7 |edition=2nd |___location=Chichester, West Sussex, England |oclc=55887497}}</ref><ref>{{Cite book |last=Frank |first=Jensen |title=Introduction to computational chemistry |date=2017 |publisher=John Wiley & Sons |isbn=978-1-118-82599-0 |oclc=989360916}}</ref> (a.k.a. continuum solvation model). These models can be used in [[computational chemistry]] to model [[solvation]] effects. COSMO has become a popular method of these solvation models in recent years. The COSMO formalism is similar to the method proposed earlier by Hoshi et al.<ref name=":0" /><ref>{{Cite journal |last1=Hoshi |first1=Hajime |last2=Sakurai |first2=Minoru |last3=Inoue |first3=Yoshio |last4=Chûjô |first4=Riichirô |date=1987-07-15 |title=Medium effects on the molecular electronic structure. I. The formulation of a theory for the estimation of a molecular electronic structure surrounded by an anisotropic medium |journal=The Journal of Chemical Physics |volume=87 |issue=2 |pages=1107–1115 |doi=10.1063/1.453343 |bibcode=1987JChPh..87.1107H |issn=0021-9606}}</ref> The COSMO approach is based -– as many other dielectric continuum models -– on the surface segmentation of a molecule surface<ref name=":3" /> (usually referred to as 'solvent accessible surface' SAS approach).

Continuum solvation models -– such as COSMO -– treat each solvent as a continuum with a [[permittivity]] ''<math>\varepsilon</math>''. Continuum solvation models approximate the solvent by a dielectric continuum, surrounding the solute molecules outside of a molecular cavity. 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 <math>q^*</math> on the surface segments. For solvents with finite dielectric constant this charge ''<math>q</math>'' is lower by approximately a factor <math>f(\varepsilon)</math>:

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==Variants and implementations==

COSMO has been implemented in a number of quantum chemistry or semi-empirical codes such as [[Amsterdam Density Functional|ADF]], [[GAMESS-US]], [[Gaussian (software)|Gaussian]], [[MOPAC]], [[NWChem]], [[TURBOMOLE]], and [[Q-Chem]]. A COSMO version of the [[polarizable continuum model]] PCM has also been developed {{Citation needed|date=April 2022}}. Depending on the implementation, the details of the cavity construction and the used radii, the segments representing the molecule surface and the <math>x</math> value for the dielectric scaling function <math>f(\varepsilon)</math> may vary - which–which at times causes problems regarding the reproducibility of published results.

==Comparison with other methods==