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

TL;DR

This paper explores fundamental unresolved issues in defining and calculating vapour-liquid surface tension, comparing virial and test transformation methods, and examining their thermodynamic consistency.

Contribution

It identifies and discusses four key open questions related to surface tension calculation methods and their thermodynamic interpretation.

Findings

Discrepancies between virial and test area methods for spherical interfaces.

Unresolved issues in relating computed surface tension to thermodynamic definitions.

The apparent kinetic contribution to surface tension remains conceptually unclear.

Abstract

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."