Direct calculation of interfacial tensions from computer simulation: Results for freely jointed tangent hard sphere chains

TL;DR

This paper introduces a new simulation-based method for calculating interfacial tensions that works for various potentials and validates it against known results, then applies it to tangent hard sphere chains.

Contribution

It develops a novel interface area sampling method for surface free energy calculation applicable to different potentials and compares theoretical predictions with simulation results for hard sphere chains.

Findings

Method agrees well with known Lennard-Jones and square well results.

Theoretical approaches vary in accuracy, with Yu and Wu's method providing excellent agreement.

Interfacial tensions for tangent hard sphere chains are successfully computed across various conditions.

Abstract

We develop a methodology for the calculation of surface free energies based on the probability distribution of a wandering interface. Using a simple extension of the NpT sampling, we allow the interface area to randomly probe the available space and evaluate the surface free energy from histogram analysis and the corresponding average. The method is suitable for studying systems with either continuous or discontinuous potentials, as it does not require explicit evaluation of the virial. The proposed algorithm is compared with known results for the surface tension of Lennard--Jones and Square Well fluid, as well as for the interface tension of a bead--spring polymer model and good agreement is found. We also calculate interfacial tensions of freely jointed tangent hard sphere chains on athermal walls for a wide range of chain lengths and densities. The results are compared with three different theoretical approaches, Scaled Particle Theory, the Yu and Wu density functional theory and an analytical approximation based on the latter approach. Whereas SPT only yields qualitative results, the last two approaches are found to yield very good agreement with simulations.