The low-lying singlet electronic excited states of HfO2: A symmetry adapted cluster–configuration interaction (SAC-CI) study

Abstract

The vertical excitation energies for the low-lying singlet excited states of the HfO2 molecule were calculated at the SAC-CI/aug-cc-pVTZ-PP level, and were compared with those of ZrO2 and TiO2. The ground electronic state (X1A1) and ten selected singlet excited states (21A1, 31A1, 11A2, 21A2, 11B1, 21B1, 31B1, 11B2, 21B2, and 31B2 states) of HfO2 were optimized at the SAC-CI/def2-SVP and SAC-CI/def2-SVPD levels. Optimized C2v structures for the ten selected states and optimized Cs structures for the 11B1 (A″), and 21A1 (A′) states were obtained. The adiabatic excitation energies for the selected excited states were calculated at the SAC-CI/def2-TZVPPD//SAC-CI/def2-SVPD level. The unrestricted density functional theory (UBPW91) was also employed to study the X1A1, 11A2, 21A2, 11B1, 21B1, and 11B2 states for comparison.