Osmotic Method for Calculating Surface Pressure of Monolayers in Molecular Dynamics Simulations

Surface pressure is a fundamental thermodynamicproperty related to the activity of molecules at interfaces. Inmolecular simulations, it is typically calculated from its definition:the difference between the surface tension of the air-water and air-surfactant interfaces. In this Letter, we show how to connect thesurface pressure with a two-dimensional osmotic pressure and howto take advantage of this analogy to obtain a practical method ofcalculating surface pressure-area isotherms in molecular simu-lation. As a proof-of-concept, compression curves of zwitterionicand ionic surfactant monolayers were obtained using the osmoticapproach and the curves were compared with the ones from thetraditional pressure tensor-based scheme. The results shown anexcellent agreement between both alternatives. Advantageously, theosmotic approach is simple to use and allows to obtain the surface pressure-area isotherm on thefly with a single simulation usingequilibration stages.

Automated summary

In this letter, the authors propose a method to connect surface pressure with two-dimensional osmotic pressure, and utilize this connection to calculate surface pressure-area isotherms in molecular simulations. By comparing with the traditional pressure tensor-based scheme, the authors demonstrate that the osmotic approach is simple, effective, and yields excellent agreement.