Unveiling geometric and electronic structures of NbSi₄−/0 clusters and electron detachments of the anionic cluster: A quantum chemical investigation

This article presents computational insights into the geometric and electronic structures of NbSi 4 −/0 clusters using density functional theory and the CASSCF/CASPT2 method. The anionic and neutral ground states are identified as the 1 A′ and 2 A′ states, respectively, within a trigonal bipyramidal isomer where the Nb atom occupies the equatorial position. The adiabatic detachment energy for the transition from the anionic ground state 1 A′ to the neutral ground state 2 A′ is estimated to be 2.30 eV. Additionally, an evaluation of the vertical detachment energies for transitions to the neutral states 1 2 A′, 1 2 A″, 2 2 A′, 2 2 A″, 3 2 A′, 3 2 A″, and 4 2 A′ yields respective values of 2.42, 2.78, 2.94, 3.34, 3.86, 4.08, and 4.28 eV. These computed electron detachment energies successfully account for all five bands observed in the photoelectron spectrum of the anionic cluster. Furthermore, the Franck–Condon factor simulations reveal extensive vibrational progressions associated with the transition to the neutral ground state 1 2 A′, manifesting as an unresolved broad band at 2.41 eV in the spectrum.