On the wavevector dependent shear viscosity of a simple fluid

Non-equilibrium molecular dynamics (NEMD) simulations employing the sinusoidal transverse force (STF) method are used to calculate the wavevector and strain rate dependent shear viscosity of a WCA fluid at a zero wavevector number density of 0.8442 and zero wavevector temperature of 0.722. The functional form of the dependence of shear viscosity on the strain rate and wavevector are examined, in the zero field limit. The ramifications of these results for the possible existence of the Burnett coefficients are discussed. The shear rate dependent viscosity for a range of wavevectors can be fitted to both a Cross analytical form and a formula derived from Quentrec's local order theory. Also it can be fitted to two square-root regimes. The extrapolated zero strain rate viscosities are consistent with a Lorentzian functional form, a Taylor series expansion in q ² and also to a q ^3/2 variation at low wavevector. This study reveals that with current computational resources it is still not possible to establish the validity of the Burnett coefficients.