A density-functional-based tight-binding scheme for the study of silicon- oxygen compounds

Abstract

Crystalline and molecular silicon-oxygen compounds are investigated using asimplified LCAO-LDA scheme for the construction of a nonorthogonal tight-binding Hamiltonian within a two-centre approximation. The repulsive part ofthe potential is derived as a universal short-range pair potential fromfitting the difference between the band structure energy of proper molecularsystems and the corresponding SCF-LDA cohesive energy curves. The methodallows, under consideration of the electronic states, molecular dynamicssimulations of large finite as well as condensed systems. The applicabilityof this method to the important class of silicon oxides and related moleculesis demonstrated. In particular, the properties of the equilibrium structureof α-quartz and several siloxane molecules are calculated and are foundto agree well with both experiment and self-consistent calculations. To obtainsuch a good agreement, it is necessary to also include the unoccupied 3dstates of Si into the LCAO basis of the wave functions.