By using the semi-empirical molecular orbital calculation code MOPAC, the structure of ringed silicate cluster such as the bond distance and bond angle of Si-O-Si, the formation free energy and infrared spectra were evaluated as a function of the number of Si. Infrared spectra of amorphous silica were experimentally observed at different temperatures, and compared with the evaluated ones by MOPAC. It was suggested that MOPAC is a useful tool for structure estimation of amorphous silica.
