The frequency dependent shear viscosity of methane

Accurate computer simulation calculations of hydrodynamic transport coefficients are notoriously expensive. In this paper we develop a method based on the non-equilibrium molecular dynamics of Ashurst and Hoover 1 which calculates the spectrum of stress-stress correlation with greater efficiency than has hitherto been possible. The calculation shows that a potential function for methane, due to Williams 2, predicts a zero frequency shear viscosity within 10 per cent of the experimental value. The spectrum of stress-stress correlation gives clear evidence of a t -3/2 long-time tail. It is shown that the spectrum is not a monotonic decreasing function of frequency. This has not been seen in computer simulation before but is in agreement with the mode-coupling prediction of Bosse et al. 3.