Quantum chemical study of the electronic structures of MnC2-/0 clusters and interpretation of the anion photoelectron spectra

Ground and Low-Lying Excited States of NbC3-/0 Clusters: Assignment of the Anion Photoelectron Spectra from Multiconfigurational Calculations

The BP86 DFT, CCSD(T), and CASPT2 methods were employed to study the low-lying states of NbC₃^-/0 clusters. The anionic and neutral ground states were determined to be the ¹A₁ and 1²A₁ of the cyclic-NbC₃^-/0 isomers. All bands in the photoelectron spectra of the NbC₃^- cluster were interpreted based on electron detachment processes from the ¹A₁ of the cyclic-NbC₃^- isomer. The X, A, B, and C bands in the spectra are, respectively, ascribed to the transitions from ¹A₁ to the 1²A₁, ²B₁, 2²A₁, and ²B₂ states. The wave function of the initial ¹A₁ anionic state exhibits a pronounced multireference character that plays to some extent a role in the ¹A₁ → 1²A₁ and the ¹A₁ → 2²A₁ ionizations. Only the ¹A₁ → ²B₂ transition appears as a clear one-electron detachment process. The Franck-Condon factor simulations for the ¹A₁ → 1²A₁ and ¹A₁ → ²B₁ transitions are consistent with the observed vibrational progressions of the X and A bands in the spectra.

Spin State Energetics of VGe n -/0 (n = 5-7) Clusters and New Assignments of the Anion Photoelectron Spectra

The geometrical structures, electron leading configurations, and relative energies of the low-lying states of VGe _n ^-/0 (n = 5-7) clusters have been investigated with density functional theory and CASSCF/CASPT2 method. The pure GGA BP86 functional gave almost the same relative energy order for the low-lying states as the CASPT2 method. At the BP86 and CASPT2 levels, the ground states of VGe _n ^-/0 (n = 5-7) clusters were proposed to be the ¹ A₁ and ² A₁ of A-VGe₅ ^-/0 , ³ A″ and ² A″, ² A' (² E₂ ) of A-VGe₆ ^-/0 , and ¹ A' and ² A' of A-VGe₇ ^-/0 isomers. The adiabatic and vertical detachment energies (ADEs and VDEs) of the detachments of one electron from several orbitals of the anionic ground states were reported at the CASPT2 level. The calculated ADEs and VDEs corresponded well with the experimental values as observed in the 266 nm anion photoelectron spectra. © 2018 Wiley Periodicals, Inc.

Computational Investigation of the Geometrical and Electronic Structures of VGen-/0 (n = 1-4) Clusters by Density Functional Theory and Multiconfigurational CASSCF/CASPT2 Method

Density functional theory and the multiconfigurational CASSCF/CASPT2 method have been employed to study the low-lying states of VGe_n^-/0 (n = 1-4) clusters. For VGe^-/0 and VGe₂^-/0 clusters, the relative energies and geometrical structures of the low-lying states are reported at the CASSCF/CASPT2 level. For the VGe₃^-/0 and VGe₄^-/0 clusters, the computational results show that due to the large contribution of the Hartree-Fock exact exchange, the hybrid B3LYP, B3PW91, and PBE0 functionals overestimate the energies of the high-spin states as compared to the pure GGA BP86 and PBE functionals and the CASPT2 method. On the basis of the pure GGA BP86 and PBE functionals and the CASSCF/CASPT2 results, the ground states of anionic and neutral clusters are defined, the relative energies of the excited states are computed, and the electron detachment energies of the anionic clusters are evaluated. The computational results are employed to give new assignments for all features in the photoelectron spectra of VGe₃^- and VGe₄^- clusters.