Comparisons between molecular dynamics and hydrodynamics treatment of nonstationary thermal processes in a liquid

Molecular dynamics (MD) and Navier-Stokes hydrodynamics have been performed to model thermal relaxation processes arising from an initially established nonequilibrium stationary state. A nanoscale two-layer Lennard-Jones (LJ) liquid system was constructed in which the two parts were initially at a different temperature, with a narrow transitional zone between the two layers that was spatially linear in temperature. The highest-temperature layer had widths of five or 20 LJ particle diameters. The hydrodynamics model used parametrized MD-derived transport coefficients and the LJ equation of state as input functions. The temporal and spatial temperature and density profiles produced by the two methods show good agreement, indicating that a hydrodynamics description is reliable even for nonstationary phenomena down to the scale of a few molecular diameters. We found that at certain locations the Navier-Stokes solution predicted that the pressure and temperature profiles relaxed in a damped oscillatory manner, which we could discern despite the fluctuations in the MD data.