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The '''test area method''' is related to the [[test volume method]] for the calculation of the [[pressure]] (which, in turn, is related to [[Widom test-particle method]]). The [[surface tension]] of a planar [[interface]] is given by the change in [[internal energy]] <math>\Delta U</math> caused by "squeezing" the system: modifying both the length in the direction normal to the interface and the area in the plane of the interface, in such a way that the total volume is left unchanged.
The '''test area method''' is related to the [[test volume method]] for the calculation of the [[pressure]] (which, in turn, is related to [[Widom test-particle method]]). The [[surface tension]] of a planar [[interface]] is given by the change in [[internal energy]] <math>\Delta U</math> caused by "squeezing" the system: modifying both the length in the direction normal to the interface and the area in the plane of the interface, in such a way that the total volume is left unchanged.


It can be shown that the surface tension, if the changes are small, is given by
It can be shown that the surface tension, if the changes are small, is given by:
<ref>[http://dx.doi.org/10.1063/1.2038827    Guy J. Gloor, George Jackson,    Felipe J. Blas and Enrique de Miguel    "Test-area simulation method for the direct determination of the interfacial tension of systems with continuous or discontinuous potentials", Journal of Chemical Physics '''123''' 134703 (2005)]</ref> (Eq. 60):
:<math> \gamma  =  - \frac{ k_B T  \Delta A } \log\langle \exp(-\Delta U/k_B T)\rangle. </math>


:<math> \gamma  =  - \frac{ k_B T }{ \Delta {\mathcal A} } \ln \langle \exp(-\Delta U/k_B T)\rangle_0. </math>
The expression parallels the one for the pressure in the [[test volume method]]; the advantages of this technique are also similar: avoidance of force calculation, easiness for discontinuous potential...


The expression parallels the one for the pressure in the [[test volume method]]; the advantages of this technique are also similar: avoidance of force calculation, easiness for discontinuous potential.
==References==
==References==
<references/>
#[http://dx.doi.org/10.1063/1.2038827    Guy J. Gloor, George Jackson,    Felipe J. Blas and Enrique de Miguel    "Test-area simulation method for the direct determination of the interfacial tension of systems with continuous or discontinuous potentials", Journal of Chemical Physics '''123''' 134703 (2005)]
[[category: computer simulation techniques]]
[[category: computer simulation techniques]]
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