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

Abstract

Density functional theory and the multiconfigurational CASSCF/CASPT2 method have been employed to study the low-lying states of VGe (n = 1-4) clusters. For VGe and VGe clusters, the relative energies and geometrical structures of the low-lying states are reported at the CASSCF/CASPT2 level. For the VGe and VGe 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 VGe and VGe clusters.

An investigation on the electronic structures of diatomic VSi0/−/+ clusters by CASSCF/CASPT2 method

“…The active space with 15 orbitals has been proven to be sufficient to study the lowlying states of VGe −/0 , VSi 3 -/0 , and VSi 4 -/0 clusters. [2,3,11] Also, most of the computer systems can handle CASSCF/CASPT2 calculations with a maximum of 15 orbitals in the active space.…”

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

“…However, the application of CASSCF/CASPT2 method is limited to very small systems because this method is computationally very expensive. The relative energies of the low‐lying states and the electron detachment energies of the anionic cluster as computed with the CASSCF/CASPT2 method prove to be sufficient to give assignments for the anion photoelectron spectroscopy . In the previous studies, all features in the photoelectron spectrum of VGe 3 − and VGe 4 − clusters were explained by the CASPT2 results.…”

“…The physical and chemical properties of transition metal‐doped germanium clusters are determined by their size, shape, and composition. In the literature, we can see a large amount of experimental and theoretical investigations on the structures of transition metal‐doped germanium clusters . It is found that doping of transition metal to pure germanium clusters can form stable cage structures that can be used as building blocks for synthesis novel materials …”

“…It was found that because of high stability, VGe 14 cluster in cage‐like O h geometry can be used as building block for developing new materials. For the VGe n −/0 ( n = 1–4) clusters, the relative energies of the low‐lying states and the electron detachment energies of the anionic clusters as computed with density functional theory and CASSCF/CASPT2 method were reported …”

“…However, the relative energy order of the low‐lying states as computed with density functional theory strongly depends on the employed functionals. In the cases of VGe 3 −/0 and VGe 4 −/0 , the hybrid B3LYP, B3PW91, and PBE0 functionals were shown to underestimate the energies of the high‐spin states due to the large contribution of the Hartree–Fock exact exchange as compared to the pure GGA BP86 and PBE functionals . Also, density functional theory cannot access to all the relevant excited states, while time‐dependent density functional theory (TD‐DFT) is less successful in accessing the low‐lying excited states of open‐shell because of the heavy spin contamination problem.…”