Modeling and LCAO Calculations of Point Defects in Crystals

Abstract

The theory of perfect crystalline solids explains those bulk properties of crystals that do not depend on boundary effects and other defects of the structure. However, real solids do not demonstrate translational symmetry. Boundaries and other regions of disruption of translational symmetry called defects are always present. Many practical applications of solids are based on the use of the properties caused by defects. By varying the defect structure of solids it is possible to change their physical and chemical properties in such a way that the defective crystals find useful applications. As an example, we mention TiO₂ crystal that has been successfully applied as a semiconductor photocatalyst with high oxidizing power and high resistance to photo- and chemical corrosion. However, the relatively large bandgap (3 eV) does not permit efficient absorption of visible light and hence prevents TiO₂ from being used in largescale environmental applications. Chemical doping of TiO₂ allows the bandgap to be reduced. The theoretical study of the doped TiO₂ helps to solve the important problem: how to best manipulate the gap while maintaining the beneficial photocatalytic properties [677].