Electronic and energy characteristics of surface centers on modified aluminosilicates containing incompletely coordinated aluminium atoms

The electronic and energy characteristics of electroneutral and charged defects on an Al/SiO/sub 2/ surface containing incompletely coordinated Al atoms have been studied in the framework of the model of orbitally stoichiometric clusters and the non-empirical PRDDO calculation scheme. The influence of the surface ionic modifiers H/sup +/, Na/sup +/, OH/sup -/, and F/sup -/ on the electron-acceptor ability of Al centers has been analyzed on the basis of the principle of an effective adjacent center formulated herein. The parameters epsilon/sub obr//sup don/, which is the energy of the highest occupied MO corresponding to a bridging oxygen atom (O/sub br/), and A/sub H+/(O/sub br/), which is the energy for the protonation of O/sub br/, have been proposed and tested as measures of the basicity of an O/sub br/ center.