Electronic states and chemical bonding in phosphate glasses

The electronic states of the phosphate glasses have been studied by the DV-Xα cluster method. The calculations have been carried out for various model clusters which are considered to exist in phosphate glasses. The energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is decreased as the cluster size is increased. The negative net charge on the bridging oxygen atoms is smaller than that on nonbridging oxygen atoms. The negative charge and the positive charge on the phosphorus atoms decrease with decreasing energy gap. The covalency of the P-O bond is increased with increasing cluster size