Visible light absorption of N-doped TiO₂ rutile using (LR/RT)-TDDFT and active space EOMCCSD calculations

We have performed detailed ground- and excited-state calculations of pure and N-doped TiO₂ rutile to model and analyze the experimentally observed UV/vis spectrum. Using our embedding model, we have performed both linear response (LR) and real-time (RT) TDDFT calculations of the excited states of the pure and N-doped systems. We have also studied the lowest excitations using high-level active space equation-of-motion coupled cluster (EOMCC) approaches involving all single and interband double excitations. We compare and contrast the nature of the excitations in detail for the pure and doped systems and also provide an analysis of the excited-state density using our RT-TDDFT calculations. Our calculations indicate a lowering of the band gap and verify the role of the N^3- states on the observed spectrum of N-doped TiO₂ rutile as suggested by experimental findings. Both RT-TDDFT and EOMCC calculations show that the excitations in pure TiO₂ are more delocalized compared with the N-doped system.