Heat conduction of lennard-jones particle system in supercritical fluid phase

The heat conduction of the three-dimensional Lennard-Jones particle system is studied using nonequilibrium molecular dynamics simulation. The geometry of the system is a rectangular parallelepiped box of L_x x L_y x L_z dimensions. Two Nosé-Hoover heat baths with different temperatures are attached to the regions near both ends of the x-direction. The density of the system and temperature of heat bath are selected so that the system is in the supercritical fluid phase. It is observed that the nonequilibrium steady state with a constant temperature gradient dT/dx and a energy (heat) flux J is realized after relaxation process from its initial configuration. The ratio of J to dT/dx denoted by κ which corresponds to the heat conductivity in the macroscopic limit is estimated for various system sizes L_x. It is confirmed that κ(L_x) shows a size dependence as expressed κ₀ + a/ √L_x and this dependence is consistent with the so-called long-time tail behavior. This κ₀ is regarded as the macroscopic conductivity. This L _x dependence implies that the heat conductivity κ(L _x) is low for a nanoscale system. The κ(L_x) of the L_x = 300 system decreases by about 10% from that of the macroscopic system.The estimated κ₀ turns out to be proportional to the density.