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

The electronic states of NbSi ( = 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 ( = 1-3) clusters were predicted as the Δ, Π, and Π states of the linear NbSi, the A, B, and B states of cyclic NbSi, and the A', A', and A″ states of tetrahedral NbSi isomers. The first feature in the photoelectron spectrum of NbSi was attributed to the transitions from the anionic Δ ground state to the neutral Π, Δ, and Φ states, whereas the second feature was assigned to the transitions to the neutral Δ, Σ, and Φ states. The first band in the photoelectron spectrum of NbSi was ascribed to the transition from the anionic A' ground state to the neutral 1A' and 1A″ states; the second band was attributed to the transitions to 2A', 2A″, and 3A' states; and the third band was assigned to the transition to 3A' states.