8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Thu 811:10-14:00P7.49Complications with the use of mechanical expressionsfor the pressure tensor and interfacial tension ininhomogeneous systemsGeorge Jackson, 1 Paul E Brumby, 1 Jose Guillermo Sampayo, 1 Andrew J.Haslam, 1 Alexandr Malijevsky, 2 Enrique de Miguel, 3 and Erich A. Muller 11 Imperial College London, Chemical Engineering, South Kensington Campus SW7 2AZ,London, United Kingdom2 Institute of Chemical Process Fundamentals of ASCR, Prague, Czech Rep3 Universidad de Huelva, Huelva, SpainWe highlight complications in the implementation of the mechanical (virial) expressions forthe computation of the pressure tensor and interfacial tension in molecular simulation of twovery different inhomogeneous systems. In the first we use test-area deformations [1] to analysevapour-liquid interfaces of LJ particles by MD simulation. For a planar interface the change infree energy due to a perturbation in the area is captured by the leading-order contribution, whichis entirely consistent with the commonly used virial relation for the surface tension. By contrastfor liquid drops one finds a large second-order contribution to the change in free energy associatedwith the energy fluctuations [2]. Since the first-order contribution in the free energy is associatedwith the standard virial route, such a mechanical relation for the surface tension is invalidatedfor small drops. In the second, we expose a versatile method to calculate the components of thepressure tensor for hard-body fluids of generic shape [3]. After considering the possible repulsivecontributions during an anisotropic system expansion, it is observed that such a volume changecan, for non-spherical molecules, give rise to configurations where overlaps occur. This featureof anisotropic molecules has to be taken into account rigorously as it can lead to discrepancies inthe calculation of tensorial contributions to the pressure, which we obtain from a series of ’ghost’anisotropic volume perturbations. For inhomogeneous systems of hard spherocylinders confinedbetween hard walls this method provides a particularly convenient route to the calculation of theinterfacial tension (surface free energy).[1] G. J. Gloor, G. Jackson, F. J. Blas, and E. de Miguel, J. Chem. Phys. 123, 134703(2005).[2] J. G. Sampayo, A. Malijevsky, E. A. Müller, E. de Miguel, and G. Jackson, J. Chem. Phys.132, 141101 (2010).[3] P. E. Brumby, A. J. Haslam, E. de Miguel, and G. Jackson, Mol. Phys. 109, 169 (2011).49