Molecular dynamics simulations of vibrational lifetimes in amorphous silicon

Recent theoretical and time resolved Raman studies disagree on the lifetime of high energy vibrational modes in amorphous silicon. The latter suggests that the lifetime increases with increasing frequency and is of the order of 10 ns for the highest frequency modes, while the former predicts a picosecond timescale that follows the two-phonon density of states. Here we present the results of molecular dynamics simulations which are complementary to the perturbative calculations. At different temperatures, kinetic energy is put into selected modes of vibration in 216 and 4096 atom systems with periodic boundary conditions and the Stillinger-Weber potential. The lifetime of medium and high frequency modes is found to be of the order of 10 ps at 5, 10 and 30 K, in qualitative agreement with the perturbative calculations.