HYBRID DENSITY-FUNCTIONAL STUDY OF THE VIBRATIONAL FREQUENCY OF A H-2MOLECULE AT THE TETRAHEDRAL SITE OF SILICON

Ab initio molecular orbital calculations based on cluster models were performed to investigate the vibrational frequency of a H-2 molecule a t a tetrahedral (T) site of Si, whose value has been controversial amo ng theoretical and experimental studies. To check the validity of the calculations, we examined the effect of the electron correlation basis set, cluster size, and anharmonicity. Among a variety of techniques t o include the electron correlation, a hybrid method that combines the Hartree-Fock (HF) method and the density-functional approach was found to give reliable results, while the HF method employed in previous st udies overestimates the frequency. The present study indicates that th e vibrational frequency of a H-2 at the T site is substantially lower than that of the free molecule, and then provides important informatio n on the identification of observed frequencies of H-2 in Si. [S0163-1 829(98)06436-4].