An <i>ab initio</i> study of self-trapped excitons in α-quartz

Abstract

The structure and properties of self-trapped excitons (STE), were investigated using density functional theory (DFT) and wave function-based [UHF, UMP2, CAS-SCF, and CCSD(T)] electronic structure methods. The DFT results were compared to those obtained using the different wave function-based electronic structure methods that treat the electron correlation and exchange with varying degrees of accuracy. The calculations were carried out on cluster configurations extracted from supercell DFT calculations of the STE in α-quartz. Two luminescent STEs were found, as well as a nonradiative state at a crossing of the singlet and triplet surfaces. One of the luminescent STEs is the same as that previously found by Fisher, Hayes, and Stoneham [J. Phys.: Condens. Matter 2, 6707 (1990)]. It was furthermore determined that the PW91 functional underestimates the energy of the triplet state, and that this error is greater with greater delocalization of the excess spin density of the state.