Equilibrium and nonequilibrium molecular dynamics methods to compute the first normal stress coefficient of a model polymer solution

Abstract

The first normal pressure (or stress) difference is directly computed from the local values of the pressure tensor components in molecular dynamics simulations of planar Poiseuille flow for a low molecular weight polymeric fluid. The resulting zero shear rate normal pressure difference agrees very well with the value computed using homogeneous shear simulations and the SLLOD algorithm, and less well with the result of the Coleman-Markowitz equation evaluated at equilibrium. This resolves doubts about the effects of homogeneous thermostats in homogeneous nonequilibrium molecular dynamics simulations.