COSMO solvation model: Difference between revisions

Revision as of 13:19, 11 January 2018

Revision as of 13:59, 11 January 2018

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==Variants and implementations==

COSMO has been implemented in a number of quantum chemistry or semi-empirical codes such as [[TURBOMOLE]], [[Gaussian (software)|Gaussian]], [[GAMESS]] and [[MOPAC]]. A COSMO version of the [[polarizable continuum model]] PCM has also been developed. Depending on the implementation, the details of the cavity construction and the used radii, the segments representing the molecule surface and the ''x'' value for the dielectric scaling function ''ƒ''(''ε'') may vary.

==Comparison with other methods==

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 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 f(''&epsilon;''). Though the scaling is an approximation, it turned out to provide a more accurate description of the so alled outlying charge, reducing the corresponding error. A method comparison<ref name=":2">{{Cite journal|last=Klamt|first=A.|last2=Moya|first2=C.|last3=Palomar|first3=J.|date=2015|title=A Comprehensive Comparison of the IEFPCM and SS(V)PE Continuum Solvation Methods with the COSMO Approach|doi=10.1021/acs.jctc.5b00601|journal=Journal of Chemical Theory and Computation|volume=11 (9)|pages=pp 4220–4225|via=}}</ref> 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 experiemntal 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.

The COSMO method is more accurate for solvents with a higher permittivity because a solvent with infinite permittivity behaves like an ideal conductor. With water (''&epsilon;''&nbsp;&asymp;&nbsp;80) a very good accuracy is achieved. Nevertheless, with the choice of ''x''&nbsp;=&nbsp;0.5 even at low permittivities it is almost as accurate as a complete solution of the electrostatic equations, though at much lower numerical costs. Apart from the numerical effciciency, another big advantage of COSMO compared to other dielectric continuum methods is its huge reduction of the artifacts caused by the small part of the electron density reaching outside of the cavity, the so-called outlying charge errors.

==See also==

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{{reflist}}

==Further reading==

* {{cite journal | author = A. Klamt, G. Schüürmann | journal = [[Journal of the Chemical Society, Perkin Transactions 2]] | year = 1993 | doi = 10.1039/P29930000799 | title = COSMO: A new approach to dielectric screening in solvents with explicit expressions for the screening energy and its gradient | pages = 799–805}}

[[Category:Computational chemistry]]