Vibrational behavior of a realistic amorphous-silicon model

The vibrational properties of a high-quality realistic model of amorphous silicon are examined. The longitudinal and transverse dynamical structure factors are calculated, and fitted to a damped harmonic oscillator (DHO) function. The width F of the best-fit DHO to the longitudinal dynamical structure factor scales approximately as k(2) for wavevectors k less than or similar to 0.55 angstrom(-1), which is above the loffe-Regel crossover frequency separating the propagating and diffusing regimes, occurring at k = 0.38 +/- 0.03 angstrom(-1). Using the DHO function as a fitting function for the transverse dynamical structure factor (without theoretical justification), gives a dependence of Gamma alpha k(alpha) with alpha similar to 2.5 for wavevectors k less than or similar to 0.7 angstrom(- 1). There was no evidence for Gamma alpha k(4) behavior for either polarization. (c) 2007 Elsevier B.V. All rights reserved.