A CASSCF/CASPT2 investigation on electron detachments from ScSi n − (n = 4–6) clusters

Structural evolution and electronic properties of neutral and anionic TiASil (A = Sc, Ti; l ≤ 12): relatively stable TiASi4 as a structural unit

Molecular orbitals (MO) and the HOMO–LUMO energy gaps (HLgs) of neutral TiASi4 clusters (A = Sc, Ti).

Structural and Electronic Properties of LaSin-/0 (n = 2-6) Clusters: Anion Photoelectron Spectroscopy and Density Functional Calculations

The structures and electronic properties of LaSi_n^- (n = 2-6) anions and their neutral counterparts were investigated by anion photoelectron spectroscopy and theoretical calculations. The vertical detachment energies of the most stable structures of LaSi_n^- (n = 2-6) were measured to be 1.28, 1.58, 2.30, 2.05, and 2.91 eV, respectively. The lowest-energy isomer of LaSi₂^- is an isosceles triangle with a C_2v symmetry. For LaSi_3-6^- clusters, the most stable isomers are polyhedrons with La atom face-capping the Si_n frameworks. The lowest-energy structures of neutral LaSi_2,4,5 clusters are similar to their anionic counterparts. The most stable isomer of neutral LaSi₃ is a planar structure with C_2v symmetry, which is different from the triangular pyramid structure of LaSi₃^- anion. The lowest-energy isomer of LaSi₆^- is a C_5v symmetric pentagonal bipyramid structure, while for neutral LaSi₆ cluster, the C_5v structure is not the most stable one. The natural population analysis showed that there is electron transfer from La atoms to Si atoms in LaSi_n^-/0 (n = 2-6). The ZZ tensor component in isochemical shielding surfaces and the anisotropy of the induced current density analyses indicate that the most stable isomer of LaSi₆^- has aromaticity.

Quantum chemistry calculations of the growth patterns, simulated photoelectron spectra, and electronic properties of LaASil (A = Sc, Y, La; l ≤ 10) compounds and their anions

The growth patterns, simulated photoelectron spectra, and electronic properties of LaASi_l (A = Sc, Y, and La; l ≤ 10) compounds and their anions were studied via quantum chemistry calculations using the Perdew-Burke-Ernzerhof (PBE) method and unprejudiced structural searching software ABCluster. The results revealed that the growth patterns of the most stable structures of neutral and anionic LaASi_l showed an adsorptive mode. The lowest-energy structures (LESs) of the LaASi_l (l ≤ 7) clusters were similar, except for those of anionic LaYSi₄^- and LaYSi₅^- and neutral LaScSi₇. Additionally, we investigated and calculated the photoelectron spectra, vertical detachment energies, adiabatic electron affinities, relative stability, charge transfer, magnetic moment, and chemical bond analysis of the LaASi_l ground-state structures. The La₂Si_l clusters exhibited higher stability than the LaYSi_l and LaScSi_l systems owing to their higher dissociation energies (DEs). The DEs of the LESs in the LaASi₃ molecule are higher than those of other clusters. Thus, the LaASi₃ cluster shows potential as a building framework for Si-based cluster materials with good stability. The natural population analysis data and chemical bond analysis results showed that the spd hybridization of the orbitals of the metal atoms in the LaASi_l system occurred. Except for the LaScSi₉ and LaScSi₁₀ clusters, the neutral LaASi_l compounds transform into the corresponding anions when an extra electron is accepted by the Si clusters.

Electronic States of CoSin-/0/+ (n = 1-3) Clusters from Density Matrix Renormalization Group-CASPT2 Calculations

Density matrix renormalization group-CASPT2 (DMRG-CASPT2), CASPT2, and density functional theory are employed to describe the complicated geometrical and electronic structures of CoSi_n^-/0/+ (n = 1-3) clusters. The active spaces of DMRG-CASPT2 are extended to 23 orbitals. The DMRG-CASPT2 method with such large active spaces is reasonable to provide highly accurate relative energies of the electronic states. The pure BP86, PBE, and TPSS functionals appear to be suitable to compute the relative energies of the electronic states of cobalt-doped silicon clusters. The leading configurations, bond distances, vibrational frequencies, normal modes, and relative energies of the electronic states are reported. The electron detachment energies of the removals of one electron from the anionic and neutral clusters are estimated. All six bands in the photoelectron spectrum of CoSi₃^- are interpreted based on the computed electron detachment energies and Franck-Condon factor simulations.

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.

Reactions of Sulfur- and Oxygen-Containing Anions with Hydrogen Atoms: A Comparative Study

Reactions of hydrogen atoms with small sulfur-containing anions, SCN^-, CH₃COS^-, C₆H₅COS^-, ^-SCH₂COOH, C₆H₅S^-, 2-HOOCC₆H₄S^-, and related oxygen-containing anions, OCN^-, CH₃COO^-, C₆H₅COO^-, HOCH₂COO^-, C₆H₅O^-, 2-HOOCC₆H₄O^-, have been studied both experimentally and computationally. The experimental results show that associative electron detachment (AED) is the only channel for the reactions. The rate constants for reactions between sulfur-containing anions and H atoms are generally higher than for the related oxygen-containing anions with the exception of the reaction of SCN^-. The generally higher reactivity of the sulfur anions contrasts with previous results where AED reactivity was found to correlate with reaction exothermicity. Density functional theory calculations indicate that the reaction enthalpies, the characteristics of the reaction potential energy surfaces, and other structural and electronic factors can influence the reaction rate constants. This study indicates that organic sulfur anions can be more reactive than related oxygen anions in the interstellar medium where hydrogen atoms are abundant.