(137f) Computing the Pressure and Interfacial Tension of Inhomogenenous Nanoscopic Systems Including Drops and Confined Anisotropic Phases: The Devil Is in the Detail

Test-area (TA) deformations [1] are used to analyse the interfacial properties of vapour-liquid interfaces of Lennard-Jones particles and TIP4P/2005 water by molecular dynamics simulation. For a planar vapour-liquid interface the change in free energy due to a perturbation in the area is captured by the leading-order contribution, which is entirely consistent with the commonly used virial (mechanical) relation for the surface tension. By contrast for liquid drops one finds a large second-order contribution to the change in free energy associated with the energetic fluctuations [2,3]. Since the first-order contribution in the free energy difference alone is associated with that obtained the standard virial relation, the mechanical route for the surface tension is invalidated for small drops. As a consequence the curvature dependence of the interfacial tension obtained with our thermodynamic TA procedure is very different to that obtained from a mechanical route, but equivalent to the corresponding calculations in grand canonical ensemble [4,5]. This additional entropic contribution has implications in its value of the tension used in classical nucleation theories. The nature of the calculation of the tensorial components of the pressure and associated surface tension of confined rod-like particles will also be discussed in relation to the virial and TA routes.

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[3] A. Malijevsky and G. Jackson, J. Phys.: Condens. Matter 24, 464121 (2012).

[4] M. Schrader, P. Virnau, and K. Binder, Phys. Rev. E 79, 061104 (2009).

[5] B. J. Block, S. K. Das, M. Oettel, P. Virnau, and K. Binder, J. Chem. Phys. 133, 154702  (2010).