We perform a series of molecular dynamics simulations of Lennard-Jones chains systems, up to tetramers, in order to investigate the influence of temperature and chain length on their phase separation and interfacial properties. Simulation results serve as a test to check the accuracy of a statistical associated fluid theory (soft-SAFT) coupled with the density gradient theory. We focus on surface tension and density profiles. The simulations allow us to discuss the success and limitations of the theory and how to estimate the only adjustable parameter, the influence parameter. This parameter is obtained by fitting the surface tension, and then used to obtain the density profiles in a predictive manner. A good agreement is found if the temperature dependence of this parameter is neglected.(c) 2004 American Institute of Physics.
Some of the pitfalls that may befall molecular simulations of interfaces are discussed. They are all related to the calculation of the pressure tensor profiles, which are needed in order to compute surface tensions. We focus on three controversial points: (1) the calculation of the pressure tensor profiles for polyatomic systems, in particular, when the SHAKE algorithm is employed, (2) the addition of long-range corrections to compensate the truncation of the potential, and (3) the importance of including adequate error intervals with the results. Most of the conclusions are general, but some specifically apply to multiple site molecular-dynamics simulations.
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