Rheology of liquid fcc metals: Equilibrium and transient-time correlation-function nonequilibrium molecular dynamics simulations

Using classical molecular dynamics simulation together with the quantum-corrected Sutton-Chen manybody embedded-atom model, we study the rheology of several liquid fcc metals (Pb, Pt, Ir, Ag, and Rh) at ambient pressure and at four temperatures ranging from 5% below the melting temperature to 75% above the melting temperature. We first carry out equilibrium molecular dynamics simulations and determine, using Green-Kubo's formalism, the shear viscosity eta(GK), the shear modulus G(infinity), and the Maxwell relaxation time tau(M). By scaling the shear stress autocorrelation function or, equivalently, the time-dependent viscosity eta(t) by eta(GK) and the time t by tau(M), we show that the scaled time-dependent viscosity for all metals collapses onto the same curve. This demonstrates that the relaxation behavior is the same for all metals studied here. We then apply transient-time correlation-function nonequilibrium molecular dynamics simulations to determine the response of liquid metals subjected to shear rates ranging from 10 s(-1) to 5 x 1012 s(-1). We show that for all metals, the shear rate-dependent viscosity eta((gamma)over dot) (scaled by eta(GK)) as a function of the applied shear rate ((gamma)over dot) scaled by the inverse of tau(M)) collapses onto the same curve. We obtain the same result for the shear rate-dependent pressure P((gamma)over dot) (scaled by G(infinity)) and for the potential energy (scaled by its equilibrium value). Fits to power-law expressions show that eta((gamma)over dot) follows the prediction of mode-coupling theory and that nonanalytic exponents are found for the shear rate dependence of pressure and potential energy.