Surface tension is central to many daily and industrial activities, ranging from washing with soap, foaming in kitchen sinks to bubble coalescence in chemical and biological reactors. The measurement of surface tension is now well established. However, the determination of surface tension by molecular simulation still remains a challenge to scientists.
Here, we have proposed an improved method for calculating surface tension of liquid-vapour interface based on the thermodynamic route. This method combines the central difference scheme used in the test-area method and the Bennett weighting factor. This improved method shows faster convergence than the test area method as the weighting factor reduces the asymmetric bias of two perturbations. When changing the perturbation magnitude, the value of surface tension obtained by this improved method agrees with the expected value with smaller errors. In addition, this method is used to calculate the surface tension of water-methanol mixtures. The values obtained agree with experimental data and other simulation data. The improved method is also used to obtain the orientation profiles at Gibbs dividing surface of water-vapour interface. The distinct bimodal profile is observed at 300K and this bimodal pattern disappears at 450K.