Local atomic structure and infrared effective charges in tetrahedrally-bonded glasses from ab initio theory electronic structure calculations

Ab initio calculations are applied to small clusters containing the elements of short range order determined from X-ray and electron diffraction radial distributions for tetrahedrally-bonded, continuous random networks glasses including SiO 2 , GeO 2 , BeF 2 , and GeS 2 . The calculations have been used to determine the dependence of the total energy on the bond-angle at the two-fold coordinated O-, F-, and S-atom sites, and the infrared effective charges for normal mode infrared active network vibrations. The results of these calculations are in excellent agreement with experiment. Of particular significance are the calculated bond angle distributions for SiO 2 and GeO 2 , which are significantly narrower than previously assumed, but in good agreement with recent modeling and experimental studies.