Probing the structural and electronic properties of bimetallic chromium-gold clusters CrmAun(m+n≤6): comparison with pure chromium and gold clusters

Structural Growth Pattern, Electronic Configurations, and Spectral and Thermochemistry Properties of ZrSnn0/-/2- (n = 4-17) Nanoscale Compounds: A Systematic Study Using Density Functional Theory

By performing density functional theory (DFT) calculations for geometric optimization in conjunction with the artificial bee colony algorithm for cluster (ABCluster) global search approach, the ground-state structures of the neutral, anionic, and dianionic ZrSnn0/-/2- (n = 4-17) nanoscale compounds are obtained. Their structural growth evolution, spectral information, and electronic and thermochemical properties are investigated. Regarding the architectural evolution of the neutral, anion, and dianionic species, ZrSnn0/-/2- (n = 4-17) compounds possess two different stages of adsorption patterns in which, when n = 4-7 and n = 8-17, ZrSn40/-/2- and ZrSn80/-/2- compounds as the basic motif adsorb Sn atoms to become the larger clusters, respectively. The simulated photoelectron spectra (PES) of anionic compounds are in good agreement with the available experimental PES. The infrared and Raman spectra can be summarized as follows: under infrared vibrational modes, the sealed cages of ZrSnn0/-/2- compounds belong to the deformation mode, and under Raman vibrational modes, they belong to the breathing mode of the Sn cage framework. The density of states (DOS) spectra and natural population analysis (NPA) indicate that the interaction between the Zr atom and Snn frameworks of capsulated compounds has been developing stronger than for unsealed compounds. The results of thermochemical properties, molecular orbital shell (MOs) analysis, and ultraviolet-visible (UV-vis) absorption spectrum indicate that the neutral ZrSn16 nanoscale compound possesses not only both thermodynamic and chemical stability but also far-infrared sensing and optoelectronic properties and hence, is the best building block motif for new multipurpose nanoscale materials.

Th2O-, Th2Au-, and Th2AuO1,2- Anions: Photoelectron Spectroscopic and Computational Characterization of Energetics and Bonding

The observation and characterization of the anions: Th₂O^-, Th₂Au^-, and Th₂AuO_1,2^- is reported. These species were studied through a synergetic combination of anion photoelectron spectroscopy and ab initio correlated molecular orbital theory calculations at the CCSD(T) level with large correlation-consistent basis sets. To better understand the energetics and bonding in these anions and their corresponding neutrals, a range of smaller diatomic to tetratomic species were studied computationally. Correlated molecular orbital theory calculations at the CCSD(T) level showed that in most of these cases, there are close-lying anions and neutral clusters with different geometries and spin states and are consistent with the experimentally observed spectra. Thus, comparison of experimentally determined and computationally predicted vertical detachment energies and electron affinities for different optimized geometries and spin states shows excellent agreement to within 0.1 eV. The structures for both the neutrals and anions have a significant ionic component to the bonding because of the large electron affinity of the Au atom and modest ionization potentials for Th₂, Th₂O, and Th₂O₂. The analysis of the bonding for the Th-Th bonds from the molecular orbitals is consistent with this ionic model. The results show that there is a wide variation in the bond distance from 2.7 to 3.5 Å for the Th-Th bonds all of which are less than twice the atomic radius of Th of 3.6 Å. The bond distances encompass bond orders from 4 to 0. There can be different bond orders for the same bond distance depending on the nature of the ionic bonding suggesting that one may not be able to correlate the bond order with the bond distance in these types of clusters. In addition, the presence of an Au atom may provide a unique probe of the bonding in such clusters because of its ability to accept an electron from clusters with modest ionization potentials.