Tight-binding quantum molecular-dynamics simulations of hydrogen in silicon

We have carried out molecular-dynamics simulations of neutral hydrogen in crystalline silicon using tight-binding (TB) quantum-mechanical total energies and forces. A well-established model due to Goodwin et al. is used for the Si-Si interactions. For the Si-H interactions, we have fit our Harrison-type TB model to the known properties of silane and to both theoretical and experimental information about hydrogen in crystalline silicon. Several simulations performed in the temperature range of 1050 to 2000 K yield a diffusion curve in good agreement with experiment. The H diffusion is found to be jumplike between bond-centered (BC) sites, and the trapping of H at the BC site is mediated by a metastable onefold coordinated H configuration which weakens adjacent Si-Si bonds, allowing the H to enter the BC site. Vibrational frequencies for hydrogen at the BC site are also calculated and isotopic frequency shifts are discussed.