Multiple time step nonequilibrium molecular dynamics simulation of the rheological properties of liquid n-decane

Nonequilibrium and equilibrium molecular dynamics simulations are reported for a united-atom model of n-decane at a state point in the liquid phase. The viscosity calculated by our nonequilibrium molecular dynamics simulations is in good agreement with that obtained from our equilibrium molecular dynamics simulations via the Green-Kubo relation and with that obtained by Mundy ct al. [J. Chem. Phys. 102, 3776 (1995)] using the same potential model at the same state conditions. Additionally, the viscosity calculated by nonequilibrium molecular dynamics is in very good agreement with experimental results for n-decane. The algorithm used for the equilibrium molecular dynamics simulations is an application to alkanes of the multitime step Nose dynamics algorithm developed by Tuckerman and Berne. For the nonequilibrium molecular dynamics simulations, an extension of the multitime step method is derived for the nonequilibrium equations of motion describing planar Couette flow with Nose thermostat. The contributions of the intramolecular interactions to the stress tensor and its relaxation have been analyzed; the bond stretching motions play a dominant role in the short-time behavior of the atomic stress-stress correlation. (C) 1996 American Institute of Physics.