Thermodynamics and transport properties of n-butane computed by molecular dynamics using a rigid interaction model.

Abstract

With a simple rigid four-center interaction model we computed the thermodynamics and transport properties of liquid n-butane by equilibrium molecular dynamics. Unlike previous works, which investigated only one state near the boiling point with semiflexible models, this work considers six states ranging from the boiling point to the triple point. In contrast to the studies based on semiflexible potential models, our calculations give good agreement with experiment for states near the boiling-point state. Reasonable agreement with experiment was achieved for the pressure and the shear viscosity at denser states near the triple point. The equilibrium time-correlation functions were computed for different shapes of the model molecules. Their time dependence leads to interesting conclusions concerning the anisotropic behavior of the molecules in the liquid state. Unlike the correlation functions, the transport coefficients were found to be nearly independent of the molecule shape. This explains partially why our rigid potential model is successful.