Stability and vibrational modes of H-2 and H-2(*) complexes in Si

Abstract

We investigate the stability and local vibrational properties of H-2 and H-2(*) complexes in Si through first-principles pseudopotential calculations within the local-density-functional approximation (LDA) and the generalized gradient approximation (GGA). We find the energy difference between H-2 and H-2(*) to be less than 0.05 eV per H atom, testing supercells containing up to 216 atoms. For the [1 0 0], [1 1 0], and [1 1 1] orientations of the Hz molecule at or near a tetrahedral site, the vibrational frequencies by the GGA for the stretch mode lie in the range of 3556-3643 cm(-1), close to the experimental value of 3618 cm(-1), while they are underestimated by about 300 cm(-1) in the LDA. A new local mode at 650-700 cm(-1) is predicted for the H-2 molecule. (C) 1999 Elsevier Science B.V. All rights reserved.