Reaction field method
The reaction field method is used in molecular simulations to simulate the effect of long range dipole-dipole interactions for simulations with periodic boundary conditions. Around each molecule there is a 'cavity' or sphere within which the Couloumb interactions are treated explicitly. Outside of this cavity the medium is assumed to have a uniform dielectric constant. The molecule induces polarization in this media which in terms create a reaction field, sometimes called the Onsager reaction field. Although Onsager's name is often attached to the technique, because he considered such a geometry in his theory of the dielectric constant,[1] the method was first introduced by Barker and Watts in 1973.[2] [3]
The effective pairwise potential becomes:
![{\displaystyle U_{AB}=q_{A}q_{B}\left[{\frac {1}{r_{AB}}}+{\frac {(\varepsilon _{RF}-1)r_{AB}^{2}}{(2\varepsilon _{RF}+1)r_{c}^{3}}}\right]}](/media/api/rest_v1/media/math/render/svg/2c1813ff1859ab5a6dd5208c3f20cb05b65aa970)
where is the cutoff radius.
Comparison to Ewald summation
The reaction field method is an alternative to the popular technique of Ewald summation. Monte Carlo simulations have been performed for dipolar anisotropic models (hard spherocylinders[4] and the Gay-Berne model for liquid crystals[5]) both indicating that the results for the reaction field and the Ewald summation are consistent. However, the reaction field presents a considerable reduction in the computer time required. The reaction field should be applied carefully, and becomes complicated or impossible to implement when studying liquid-vapour coexistence or phase transitions.[6]
References
- ^ Onsager, Lars (1 August 1936). Journal of the American Chemical Society. 58 (8): 1486–1493. doi:10.1021/ja01299a050.
{{cite journal}}:|access-date=requires|url=(help); Missing or empty|title=(help) - ^ Barker, J.A. (1 September 1973). "Monte Carlo studies of the dielectric properties of water-like models". Molecular Physics. 26 (3): 789–792. doi:10.1080/00268977300102101.
{{cite journal}}:|access-date=requires|url=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Watts, R.O. (1 October 1974). "Monte Carlo studies of liquid water". Molecular Physics. 28 (4): 1069–1083. doi:10.1080/00268977400102381.
{{cite journal}}:|access-date=requires|url=(help) - ^ GIL-VILLEGAS, By ALEJANDRO (1 November 1997). "Reaction-field and Ewald summation methods in Monte Carlo simulations of dipolar liquid crystals". Molecular Physics. 92 (4): 723–734. doi:10.1080/002689797170004.
{{cite journal}}:|access-date=requires|url=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ MOHAMMED HOUSSA ABDELKRIM OUALID LU (1 June 1998). "Reaction field and Ewald summation study of mesophase formation in dipolar Gay-Berne model". Molecular Physics. 94 (3): 439–446. doi:10.1080/002689798167944.
{{cite journal}}:|access-date=requires|url=(help) - ^ Benito Garzón, Santiago Lago and Carlos Vega "Reaction field simulations of the vapor-liquid equilibria of dipolar fluids: Does the reaction field dielectric constant affect the coexistence properties?", Chemical Physics Letters 231 pp. 366-372 (1994)
Further reading
- Martin Neumann and Othmar Steinhauser "The influence of boundary conditions used in machine simulations on the structure of polar systems", Molecular Physics 39 pp. 437-454 (1980)
- Martin Neumann, Othmar Steinhauser and G. Stuart Pawley "Consistent calculation of the static and frequency-dependent dielectric constant in computer simulations", Molecular Physics 52 pp. 97-113 (1984)
- Andrij Baumketner "Removing systematic errors in interionic potentials of mean force computed in molecular simulations using reaction-field-based electrostatics", Journal of Chemical Physics 130 104106 (2009)
- Reaction Field method
 | This chemistry-related article is a stub. You can help Wikipedia by expanding it. |