On the Spectroscopic Modeling of Localized Defects in Sodalites by TD-DFT

In this work, we designed a simulation protocol to investigate the spectroscopic properties of point defects in sodalite minerals, Na₈Si₆Al₆O₂₄Cl₂, using time-dependent density functional theory. The F-center absorption spectrum and the sulfur impurity’s (S₂–) fluorescence spectrum were simulated by considering different electrostatic environments around the cluster (embedded cluster model, ECM approach) and by coupling the electronic transition with vibrations obtained at the periodic boundary condition (PBC) level. These results highlight the influence of vibronic coupling in these spectra and of the confinement in the case of S₂– fluorescence. The performances of 17 density functionals were assessed for the calculation of vertical excitation and emission energies against experimental values; global hybrids and generalized gradient approximation (GGA) gave the best results. The impact of chemical composition on the absorption spectra of the F-center was investigated, allowing the simulation of colors in absorption for 12 materials from the sodalite family.