AB-INITIO CALCULATIONS ON POSSIBLE HARD MATERIALS BASED ON INTERPENETRATING NETWORKS - SIO2-CENTER-DOT-BEF2

The energetics and electronic behavior of SiO2 . BeF2, based on interp enetrating diamondoid nets and recently proposed as a possible hard ma terial, have been studied with ab initio periodic LCAO Hartree-Fock me thods. The composite compound turns out to be unstable with respect to the precursors SiO2 and BeF2. The origin of the instability has been analyzed with the aid of crystal orbital displacement (COD) plots. A b ulk modulus close to the sum of those of the two precursors is calcula ted for SiO2 . BeF2. The additivity of the bulk moduli of subnets sugg ests that hard precursors should be required to obtain superhard mater ials.