Test area method

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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 \Delta U 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:

 \gamma  =  - \frac{ k_B T  \Delta A } \log\langle \exp(-\Delta U/k_B T)\rangle.

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

  1. 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)