We present anab initiocalculation of the infrared vibrational spectrum of amorphous silicon. The electron polarization, which is the main ingredient to obtain the infrared spectra, is evaluated using the recent formulation in terms of Berry’s phase, while the time evolution of the system is studied using Car–Parrinello molecular dynamics. Our results are in quantitative agreement with experimental data and also with the results of empirical calculations based on a bond-dipole model. ©1997 American Institute of Physics.