Energetic and vibrational analysis of hydrogenated silicon m vacancies above saturation

We present a systematic study on hydrogenated silicon $m$ vacancies above saturation. For each system a global geometry optimization search for low-lying local minima is performed using a newly developed SiH tight binding model. Subsequently a large number of low-energy structures are examined by density functional calculations using a minimal basis set. Finally the energetically favorable structures are reexamined using a systematically extendable basis set with local, semilocal, and hybrid exchange-correlation functionals. Particular attention is paid to the divacancy to which the Raman peak at 3822 ${\mathrm{cm}}^{\ensuremath{-}1}$ associated with the ${\mathrm{H}}_{2}$ molecule had previously been assigned. Both the energetics and vibrational analysis of divacancy-related stable configurations suggest a revision of the above conclusion.