TRANSIENT HEAT-TRANSFER IN A LENNARD-JONES CRYSTAL BY MOLECULAR-DYNAMICS

The phenomenological description of heat conduction problems in non-co ntinuous media by the Fourier law, is called into question when therma l transfers are studied at both temporal and space microscales. Severa l Equilibrium and Non Equilibrium Molecular Dynamics (EMD and NEMD) ex periments have been carried out in order to specify the nature of the heat transfer al short times in a Lennard-Jones solid. Presented are ( i) the hydrodynamic, the heat flux and the phonon relaxation times (re spectively tau(H), tau(nu) and tau(P)) computations done thanks to EMD experiments, tau(nu) is deduced from a heat flux fluctuations descrip tion, and tau(P) is worked out from the Peierls thermal conductivity d efinition in the frame of the Deybe model. (ii) The response of the la ttice to a kinetic energy step which displays wave-like phenomena of c oherent and incoherent nature for times of the order of some phonon re laxation times, An analysis in terms of mode velocities confirms the p resence of acoustic and thermal (second sound) wave propagation.