ABINITIO MOLECULAR-ORBITAL CALCULATION OF THE INTERATOMIC POTENTIAL AND FORCE-CONSTANTS IN SILICON OXYNITRIDE GLASS

Ab initio molecular orbital calculation was applied to the model molecule from the framework structure of silicon oxynitride glass to determine chemical bonding parameters with special attention to the nitrogen atom. The dependence of the potential energy on the bridging bond length and the bond angle was calculated for the model molecule in the range of the geometry close to those for the minimum energy configuration. The bending force constant K// theta was 97. 3 N/m, while K//r equals 507 N/m was obtained as the stretching force constant. The K// theta value for the N left bracket Si(OH)//3 right bracket //3 was much greater than the Si-O-Si bending force constant for the (HO)//3SiOSi(OH)//3 model molecule. The frequencies of the normal vibration calculated from these force constants were in accord with that corresponding to the same vibrational mode observed in the infrared spectra of the silicon oxynitride.