(34f) Rheology of Liquid Metals: Nonequilibrium Molecular Dynamics Simulations at Experimentally Accessible Shear Rates

The knowledge of the transport properties are essential to understand the behavior of liquids and supercooled liquids. These properties are important in a wide range of applications, from biological systems to materials processing. Nonequilibrium molecular dynamics (NEMD) simulations provides, in principle, a direct access to the microscopic structural changes induced by the applied shear rate. It is therefore a valuable tool to understand how the structure and in turn the transport properties of liquids are affected by shear. However, conventional NEMD methods only allow one to study systems subjected to very large shear rates, several orders of magnitude larger than the experimentally accessible rates. These methods only provide insight into the non-Newtonian behavior of liquids. For instance, in their NEMD study of liquid copper [1], Xu et al. noted that the shear rates explored by NEMD simulations were at least of the order of 1010  s?1 and mostly one to two orders of magnitude larger. As a result, in their simulations, liquid copper exhibited a pseudoplastic fluid behavior and underwent shear thinning over the range of shear rates simulated.

The aim of this work is to address the inability of conventional NEMD methods to study the response of a liquid subjected to experimentally accessible shear rates. For this purpose, we consider the so-called transient time correlation function (TTCF) formalism. The TTCF formalism is essentially a nonlinear generalization of the Green?Kubo relations. We show how this approach can be extended to study the response of liquid metals, modeled by a many-body embedded atom model (EAM) potential and subjected to a realistic shear rate [2]. Our simulations provide a full picture of the rheology of the system, in the Newtonian regime as well as in the shear-thinning regime.

[1] P. Xu, T. Cagin and W. A. Goddard, J. Chem. Phys. 123, 104506 (2005).

[2] C. Desgranges and J. Delhommelle, J. Chem. Phys. 128, 084506 (2008).