Molecular-dynamics approach for determining the vacancy heat of transport

We develop an approach for using equilibrium and nonequilibrium molecular-dynamics simulations to determine the heat of transport of a vacancy in a Lennard–Jones fcc crystal. The approach depends on computing the entropy and internal energy changes that accompany the hopping of a vacancy either parallel or antiparallel to a temperature gradient. We find that the internal energy, expressed in terms of the vacancy formation energy, is essentially unchanged during vacancy hops. However, we show that entropy is generated during vacancy hops, indicating the presence of dissipative processes. We show theoretically how the computation of the entropy generation is directly related to the reduced heat of transport. From an estimate of the enthalpy of vacancy formation, we determine the heat of transport, which is found to be positive in contradiction to previously-published results using a different method. The heat of transport we predict is quite close to the enthalpy of vacancy formation.