Determination of the origin and magnitude of logarithmic finite-size effects on interfacial tension: role of interfacial fluctuations and domain breathing.

The ensemble-switch method for computing wall excess free energies of condensed matter is extended to estimate the interface free energies between coexisting phases very accurately. By this method, system geometries with linear dimensions L parallel and Lz perpendicular to the interface with various boundary conditions in the canonical or grand canonical ensemble can be studied. Using two- and three-dimensional Ising models, the nature of the occurring logarithmic finite-size corrections is studied. It is found crucial to include interfacial fluctuations due to "domain breathing."