Subtleties in the calculation of the pressure and pressure tensor of anisotropic particles from volume-perturbation methods and the apparent asymmetry of the compressive and expansive contributions

Paul E Brumby (1) , Andrew J. Haslam (1) , Enrique de Miguel (2) , George Jackson (1)

1 Chemical Engineering
2 Applied Physics

An effcient and versatile method to calculate the components of the pressure tensor for hard-body fluids of generic shape from the perspective of molecular simulation is presented. After due consideration of all the possible repulsive contributions exerted by molecules upon their surroundings during an anisotropic system expansion, it is observed that such a volume changevcan, for non-spherical molecules, give rise to configurations where overlaps occur. This feature of anisotropic molecules has to be taken into account rigorously as it can lead to discrepanciesvin the calculation of tensorial contributions to the pressure. Using the condition of detailedvbalance as a basis, a perturbation method developed for spherical molecules has been extendedvso that it is applicable to non-spherical and non-convex molecules. From a series of 'ghost' anisotropic volume perturbations the residual contribution to the components of the pressure tensor may be accurately calculated. Comparisons are made with prior methods, and where relevant results are evaluated against existing data. For inhomogeneous systems this method provides a particularly convenient route to the calculation of the interfacial tension (surface free energy) from molecular simulations.

Mots clés: Physical Sciences

Paul E Brumby, Andrew J. Haslam, Enrique de Miguel, George Jackson. Subtleties in the calculation of the pressure and pressure tensor of anisotropic particles from volume-perturbation methods and the apparent asymmetry of the compressive and expansive contributions. Molecular Physics, 2010, pp.1. ⟨10.1080/00268976.2010.530301⟩. ⟨hal-00650359⟩