The most naive perturbation method to estimate interfacial free energies is based on the assumption that the interface between coexisting phases is infinitely sharp. Although this approximation does not yield particularly accurate estimates for the liquid-vapor surface tension, we find that it works surprisingly well for the interface between a dense liquid and a solid. As an illustration we estimate the liquid-solid interfacial free energy of a Lennard-Jones system with truncated and shifted interactions and compare the results with numerical data that have been reported in the literature. We find that the agreement between theory and simulation is excellent. In contrast, if we apply the same procedure to estimate the variation of the liquid-vapor surface tension, for different variants of the Lennard-Jones potential (truncated/shifted/force-shifted), we find that the agreement with the available simulation data is, at best, fair. The present method makes it possible to obtain quick and easy estimate of the effect on the surface free energy of different potential-truncation schemes used in computer simulations.
Mol. Simul.

Valeriani, C., Wang, Z.-J., & Frenkel, D. (2007). Comparison of simple perturbation-theory estimates for the liquid-solid and the liquid-vapor interfacial free energies of Lennard-Jones systems. Mol. Simul., 33, 1023–1028. doi:10.1080/08927020701579352