Calculation of vibrational lifetimes in amorphous silicon using molecular dynamics simulations

The decay of normal-mode excitations is calculated for amorphous silicon through molecular-dynamics simulations within periodic supercells consisting of 216 and 4096 atoms. Phenomenological structural and interatomic potential models are employed. At moderate temperatures, lifetimes are found to be on the order of 10 ps and lifetimes of localized and extended nonpropagating modes are comparable. These features are in agreement with related perturbation theory calculations, and in strong disagreement with the frustrated anharmonic decay predicted by the fracton model and apparently with the results of anti-Stokes Raman experiments performed at $T=10\mathrm{}$ K.