Open questions on defining and computing the vapour-liquid surface tension by virial and test transformation approaches

This work addresses four problems in defining and computing the surface tension of vapour-liquid interfaces: (1) The apparent kinetic contribution to the surface tension, and what it is that makes it appear; (2) the problem of defining the local virial, which for some purposes appears to be necessary; (3) the disagreement between results for spherical interfaces when using different methods, specifically the virial and the test area method; (4) how the surface tension values obtained from these methods can be related to the definition of the surface tension from thermodynamics - since if they cannot, it is a meaningless exercise to compute them. At the end, all these problems remain unsolved: They are “open questions.”