TRANSVERSE-CURRENT AUTOCORRELATION-FUNCTION CALCULATIONS OF THE SHEAR VISCOSITY FOR MOLECULAR LIQUIDS

The usual approach to calculating shear viscosities and other thermal transport coefficients from equilibrium molecular-dynamics simulations has been to evaluate the appropriate Green-Kubo relation. An alternative to this method is to examine the long-time behavior of correlations formed from the amplitudes of spontaneous fluctuations in transverse momentum fields (transverse-current autocorrelation functions). For systems in the hydrodynamic limit, long-wavelength fluctuations in transverse momentum fields decay exponentially with a decay constant l/tau(H)=mu k(2)/rho, where k is the wave vector of the fluctuation, mu is the shear viscosity, and rho is the density. Thus, determination of tau(H), leads directly to mu. This approach is used to calculate the shear viscosity for the Lennard-Jones fluid, liquid carbon dioxide, and the TIP4P model of water of Jorgensen et al.