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 Γ of the best-fit DHO to the longitudinal dynamical structure factor scales approximately as k2 for wavevectors k ≲ 0.55 Å−1, which is above the Ioffe–Regel crossover frequency separating the propagating and diffusing regimes, occurring at k = 0.38 ± 0.03 Å−1. Using the DHO function as a fitting function for the transverse dynamical structure factor (without theoretical justification), gives a dependence of Γ ∝ kα with α ∼ 2.5 for wavevectors k ≲ 0.7 Å−1. There was no evidence for Γ ∝ k4 behavior for either polarization.