First principles studies of H in diamond

Ab initio methods are used to investigate hydrogen defects in diamond. For the isolated impurity, the bond-centered site is found lowest in energy and posses both donor and acceptor levels. The neutral defect possesses a sing le local mode with very small infrared effective charge, but the effective charge for the negative charge state is much larger. H+ is calculated to be very mobile with a low activation barrier. Hydrogen dimers are stable as H *(2) defects which are also found to be almost IR-inactive. The complex bet ween B and H is investigated and the activation energy for the reaction B-H --> B- + H+ found to be in rasonable agreement with experiment. Hydrogen i s strongly bound to dislocations which, together with H*(2) may form part o f the hydrogen accumulation layer detected in some plasma studies.