The relationship between atomic displacement factors and structural parameters in silica polymorphs

Multiple linear regression analysis of the equivalent isotropic displacement factor, at room T, of oxygen atoms or silicon atoms as dependent variable, and of numerous structural parameters as independent variables, has been applied to a sample of 138 symmetrically independent O atoms and a sample of 71 symmetrical independent Si atoms from 7 phases of SiO (sub 2) . More than 80% of the variation of the equivalent isotropic displacement factor for Si is accounted for in terms of variation of structural parameters. A strong connection appears to exist between the thermal motions of O and Si and the type of chemical bond, with a positive correlation with the electrostatic site energy of O, and a negative correlation for Si. Both displacement factors are positively correlated to the fractional s-character of Si and O in the Si-O bond.