A common fingerprint of the electrically active point defects in semiconductors was the transition between their localized defect states upon excitation, which may result in characteristic absorption or photoluminescence spectrum. While density functional calculations were very successful in exploring the ground-state properties like formation energies or hyperfine tensors the density functional theory, in principle, was not capable of providing reliable excitation spectrum. Time-dependent density functional theory, however, addresses this issue which made it possible to study the properties of point defects associated with their excited states. Time-dependent density functional theory was applied here to two characteristic examples: the well-known nitrogen-vacancy defect in diamond and the less well-known divacancy in silicon carbide. The former defect was a leading candidate in solid-state quantum bit applications where detailed knowledge about the excitation spectrum was extremely important. The excitation property of the divacancy was also studied and its relevance in different applications was considered.

Time-Dependent Density Functional Study on the Excitation Spectrum of Point Defects in Semiconductors. A.Gali: Physica Status Solidi B, 2011, 248[6], 1337–46