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 1/τH={μ}k²/{ρ}, where k is the wave vector of the fluctuation, {μ} is the shear viscosity, and {ρ} is the density. Thus, determination of τH leads directly to {μ}. 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. [J. Chem. Phys. 79, 926 (1983)].