Calculation of soft atomic potentials formed by three-center bonds in germanosilicate glass

Properties of the neutral, singly and doubly negatively charged =Ge-O-Ge= linkages and of the neutral =Si-O-Ge= linkage stretched from 0.34 to 0.46 nm in vitreous silicon dioxide are studied in an isolated molecular cluster model with quantum-chemical methods. The soft atomic potential caused by the formation of three-center bonds between atoms of the linkage is found to arise in the neutral =Ge-O-Ge= linkage stretched to approximate to 0.40 nm. No soft potential is formed in the =Si-O-Ge= linkage and in the singly negatively charged =Ge-O-Ge= linkage. Capture of a pair of electrons in the =Ge-O-Ge= linkage results in softening orf the atomic potential, the soft potential and the three-center bond being formed in the linkage stretched even to 0.38 nm. Results of calculations of electronic structures of the three-center bonds and vibrational properties of the stretched neutral and charged =Ge-O-Ge= linkages are discussed. (C) 1998 Elsevier Science B.V.