Anharmonic phonon response in aluminum: A neutron-scattering test of computer-simulation calculations

Abstract

In contrast to the three finite-frequency peaks in the dynamical structure factor $S(\stackrel{\ensuremath{\rightarrow}}{\mathrm{Q}},\ensuremath{\omega})$ predicted in a recent computer-simulation study of aluminum at 800 K, the line shape observed by means of neutron scattering is smooth and exhibits a single narrow peak at each wave vector. The observed line shape is, however, in agreement with approximate analytical calculations based on self-consistent-phonon theory, using the same interatomic force model as employed in the computer simulation. These comparisons suggest that exact computer simulation on a finite lattice can produce artifical peaks or oscillations not characteristic of the real solid. We find that these artificial peaks are associated with long-time noise in the computer simulation of $S(Q,t)$; their effect on $S(Q,\ensuremath{\omega})$ can be minimized by use of a damping function.