Electronic structures of NbGen−/0/+ (n = 1–3) clusters from multiconfigurational CASPT2 and density matrix renormalization group‐CASPT2 calculations

• Published in: Journal of computational chemistry 2020-12, Vol.41 (31), p.2641-2652
• Main Authors: Tran, Van Tan, Tran, Quoc Tri
• Format: Article
• Language: English
• Subjects: CASPT2; Clusters; Density functional theory; detachment energies; DMRG‐CASPT2; electronic states; Ground state; Isomers; Mathematical analysis; NbGen−/0/+ (n = 1–3) clusters; relative energies
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.26420

Density functional theory and multiconfigurational CASPT2 and density matrix renormalization group DMRG‐CASPT2 have been employed to study the low‐lying states of NbGen−/0/+ (n = 1–3) clusters. With the DMRG‐CASPT2 method, the active spaces are extended to a size of 20 orbitals. For most of the states, the CASPT2 relative energies are comparable with the DMRG‐CASPT2 results. The leading configuration, bond distances, vibrational frequencies, and relative energies of the low‐lying states of these clusters were calculated. The ground states of these clusters were computed to be 3Δ, 4Φ, and 5Φ of NbGe−/0/+; 3A2, 4B1, and 3B1 of cyclic‐NbGe2−/0/+; and 1A′, 12A″ and 12A′′ (2E), and 3A″ of tetrahedral‐NbGe3−/0/+ isomers. For NbGe cluster, our calculations proposed that the 6∑ is almost degenerate with the 4Φ with the CASPT2 and DMRG‐CASPT2 relative energies of 0.05 and 0.06 eV. The adiabatic detachment energies of NbGen− (n = 1–3) clusters were estimated to be 1.46, 1.55, and 2.18 eV by the CASPT2 method. The relevant detachment energies of the anionic ground state and the ionization energies of the neutral ground states are evaluated at the CASPT2 level. The ground states of NbGen−/0 (n = 1–3) clusters are predicted to be the 3Δ and 4Φ of NbGe−/0, 3A2 and 4B1 of cyclic‐NbGe2−/0, and 1A′ and 12A″, 12A″ (2E) of tetrahedral‐NbGe3−/0 isomers by the BP86 functional, CASPT2, and density matrix renormalization group‐CASPT2 method. The adiabatic detachment energies of the ground states of NbGen− (n = 1–3) clusters are estimated to be 1.46, 1.55, and 2.18 eV at the CASPT2 level. The highest occupied molecular orbitals of the anionic ground states from which one electron is removed are determined.