Approach-to-equilibrium molecular dynamics
Résumé
Besides steady-state methods presented in Chapters 8 and 9, molecular dynamics simulations can also be used to simulate temperature transients, by means of approach-to-equilibrium molecular dynamics (AEMD) calculations. The interest for such methods is materialso the short MD simulation time required to studThe commont, compareof to a steady state. Temperature transients can be used to calculate thermal boundary resistances under the lumped capacitance approximation, valid when a high resistance separates two good thermal conductors (Shenogin, 2004). The approach-to- equilibrium of an instantaneously heated portion of a supercell has also been used to obtain the thermal conductivity of a system of molecules (Hulse, 2005). In the present work, we present a 192variation of these transient methods where two separate blocks are equilibrated at different temperatures before the approach-to-equilibrium is monitored to extract a characteristic decay time (Section 8.2). In parallel, the heat equation is solved analytically under the same conditions of periodicity and initial temperature profile (Section 8.3). It is shown that the temperature profile obtained by MD has the spatial and temporal form of the Fourier series solution of the heat equation. The same relation between the transient time and the thermal conductivity is therefore used to calculate the thermal conductivity of the atomic system. An application to the case of a crystal is shortly recalled in Section 8.4. The approach is also applied to an amorphous material, amorphous silica, and the differences of time scale and length dependences are discussed (Section 8.5). © 2017 Pan Stanford Publishing Pte. Ltd.