Accurate determination of normal stress differences via transient-time correlation function - non-equilibrium molecular dynamics (TTCF-NEMD) simulations

When a non-Newtonian liquid undergoes shear flow, differences between the values taken by the diagonal elements of the pressure tensor arise. These differences, known as normal stress differences, are notoriously difficult to compute accurately. In this work, we propose to apply the transient-time correlation function (TTCF) formalism together with non-equilibrium molecular dynamics (NEMD) simulations to determine normal stress differences, as well as the corresponding normal stress coefficients, in an atomic fluid undergoing shear flow. Our results shed light on the dependence of normal stress differences and coefficients on the applied shear.