[[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" /> ('''CO'''nductorCOnductor-like '''S'''creeningScreening '''MO'''delMOdel) 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 |url=http://dx.doi.org/10.1002/wcms.1519 |journal=WIREs Computational Molecular Science |volume=11 |issue=4 |doi=10.1002/wcms.1519 |issn=1759-0876}}</ref><ref>{{Cite book |last=Cramer |first=Christopher J. |url=https://www.worldcat.org/oclc/55887497 |title=Essentials of computational chemistry : theories and models |date=2004 |publisher=Wiley |isbn=0-470-09182-7 |edition=2nd ed |___location=Chichester, West Sussex, England |oclc=55887497}}</ref><ref>{{Cite book |last=Frank |first=Jensen, |url=http://worldcat.org/oclc/989360916 |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 |last=Hoshi |first=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 |url=http://dx.doi.org/10.1063/1.453343 |journal=The Journal of Chemical Physics |volume=87 |issue=2 |pages=1107–1115 |doi=10.1063/1.453343 |issn=0021-9606}}</ref>. The COSMO appraoch 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 appraoch).
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.
