Comparative study of vibrational frequencies of H-2 molecules in Si and GaAs

First-principles calculations are performed to obtain vibrational frequencies of H-2 molecules in crystalline GaAs and in Si based on the generalized gradient approximation (GGA) as well as the local-density approximation (LDA) in the density-functional theory. We find, in both Si and GaAs, that the tetrahedral interstitial site is energetically favorable for the H-2 molecule and that the vibrational frequency of the H-2 molecule shows a substantial downward shift compared with that of a free H-2 molecule. providing a microscopic identification of the Raman and the infrared-absorption spectra recently observed in the materials. We also find that the calculated values by the GGA are in better agreement with the experimental data than the LDA. [S0163-1829(97)51840-6].