Electron Detachments of NbSi n -/0 ( n = 1-3) Clusters from Density Matrix Renormalization Group-CASPT2 Calculations.

The electronic states of NbSi n -/0/+ ( n = 1-3) clusters have been explored using the state-of-the-art DMRG-CASPT2 method with relatively large active spaces. The leading configurations, bond distances, vibrational frequencies, and relative energies of the low-lying states were identified. Electron detachment energies of the anionic cluster and ionization energies of the neutral clusters were reported at the DMRG-CASPT2 level. The ground states of the NbSi n -/0/+ ( n = 1-3) clusters were predicted as the 3 Δ, 4 Π, and 5 Π states of the linear NbSi -/0/+ , the 3 A 2 , 4 B 1 , and 3 B 1 states of cyclic NbSi 2 -/0/+ , and the 1 A', 2 A', and 3 A″ states of tetrahedral NbSi 3 -/0/+ isomers. The first feature in the photoelectron spectrum of NbSi - was attributed to the transitions from the anionic 3 Δ ground state to the neutral 4 Π, 4 Δ, and 4 Φ states, whereas the second feature was assigned to the transitions to the neutral 2 Δ, 2 Σ + , and 2 Φ states. The first band in the photoelectron spectrum of NbSi 3 - was ascribed to the transition from the anionic 1 A' ground state to the neutral 1 2 A' and 1 2 A″ states; the second band was attributed to the transitions to 2 2 A', 2 2 A″, and 3 2 A' states; and the third band was assigned to the transition to 3 2 A' states.