Dynamics of bgr;hyphen;Quartz Structures of Vitreous SiO2and BeF2

摘要

The optically active vibrational modes of vitreous SiO2and BeF2were calculated using the bgr;hyphen;quartz models determined for these materials from recent xhyphen;ray diffraction experiments. The assumption of regular bgr;hyphen;quartz lattice models with the appropriate unit cell parameters resulted in good agreement between observed and calculated frequencies. The crystal potential functions of SiO2and BeF2were derived from a modified valence force field, and several force fields which differed in the type of interaction terms allowed were studied. Calculated mean amplitudes forSisngbnd;OandBesngbnd;Fstretching motion and forOmiddot;middot;middot;O,thinsp;Simiddot;middot;middot;Si,thinsp;Fmiddot;middot;middot;F,thinsp;andthinsp;Bemiddot;middot;middot;Benonbonded displacements were in good agreement with the respective mean amplitudes derived from the xhyphen;ray data.