Rheology Of Liquid Fcc Metals: Equilibrium And Transient-time Correlation-function Nonequilibriummolecular Dynamics Simulations

摘要

Using classical molecular dynamics simulation together with the quantum-corrected Sutton-Chen many-body 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 η_(GK), the shear modulus G_x, and the Maxwell relaxation time τ_M. By scaling the shear stress autocorrelation function or, equivalently, the time-dependent viscosity η(t) by η_(GK) and the time t by τ_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 × 10~(12) s~(-1). We show that for all metals, the shear rate-dependent viscosity η(γ) (scaled by η_(GK)) as a function of the applied shear rate γ (scaled by the inverse of τ_M) collapses onto the same curve. We obtain the same result for the shear rate-dependent pressure P(γ) (scaled by G_∞) and for the potential energy (scaled by its equilibrium value). Fits to power-law expressions show that η(γ) follows the prediction of mode-coupling theory and that nonanalytic exponents are found for the shear rate dependence of pressure and potential energy.