Energy and pressure of shearing fluids at different state points

Abstract

Nonequilibrium molecular dynamics simulations are reported at different strain rates (gamma) and thermodynamic state points for a shearing atomic fluid interacting via a Lennard-Jones potential. Our simulations are performed at the Lennard-Jones triple point, a point midway between the triple point and the critical point, and a high point closer to the critical temperature. We find that, for the mid-point and high point, the energy and hydrostatic pressures have strain-rate dependencies of gamma(2), in contrast to the gamma(3/2) dependencies predicted by mode coupling theory. This analytical dependence is consistent with a Taylor series expansion of these quantities as powers of the strain rate tensor. Only at the triple point does the pressure and energy display a nonanalytical dependence on gamma(3/2).

Spatial correlations of hydrodynamic fluctuations in simple fluids under shear flow: A mesoscale simulation study

“…However, in atom-scale simulations using two-and three-body potentials, the exponent was observed to be ζ ≈ 2.0 away from the triple point [35]. The deviation was ascribed to two-body interactions [36,37]. Further systematic studies using the Lenard-Jones potential found the exponent in the range ζ = 1.2-2.0 as a function of density and temperature [38], thereby rendering ζ = 3/2 only a special case.…”

Nonequilibrium equation of state for Lennard‐Jones fluids and the calculation of strain‐rate dependent shear viscosity

“…The α = 3/2 exponent is consistent with both mode‐coupling theory9 and simulation data at the triple point of the 12‐6 Lennard‐Jones fluid. However, nonequilibrium molecular dynamics (NEMD) simulation data12–14 for the pressure of a fluid under shear away from the triple‐point indicates that the value of α varies continuously from 1.2 to 2 depending both on temperature and density.…”

Parallelisation of Nonequilibrium Molecular Dynamics Code for Polymer Melts Using OpenMP

“…After this value, they increase rapidly as the shear rate increases. For simple fluids, NEMD simulations have demonstrated that the pressure or energy as a function of shear rate under planar shear flow follows a power law [15,16]. The results from this study seem unlikely to give such a simple relationship for long chain systems.…”