TRANSVERSE-CURRENT AUTOCORRELATION-FUNCTION CALCULATIONS OF THE SHEARVISCOSITY 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 alternat ive to this method is to examine the long-time behavior of correlation s formed from the amplitudes of spontaneous fluctuations in transverse momentum fields (transverse-current autocorrelation functions). For s ystems in the hydrodynamic limit, long-wavelength fluctuations in tran sverse 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 ta u(H), leads directly to mu. This approach is used to calculate the she ar viscosity for the Lennard-Jones fluid, liquid carbon dioxide, and t he TIP4P model of water of Jorgensen et al.