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Density functional theory approaches are employed to elucidate the structural features and electronic properties of cis-dioxidomolybdenum(VI) complexes with water, 8-hydroxyquinoline and 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one. Geometrical parameters are optimized using B3PW91, B3LYP functionals in conjunction with def2-TZVP, LanL2DZ and 6-311 + G basis sets. Computed results show that the complex energetically prefers a pseudo-pentagonal bipyramidal shape in the ground state. The nature of intramolecular interactions between Mo(VI) and ligands is evaluated by analyzing the natural bond orbital and quantum theory of atoms in molecules. The Mo–OH2 interaction is rather weak with an average distance of 2.445 Å and a very low Mayer bond order of 0.235. The vibrational signatures and vertical electronic transitions of some excitations are examined and compared to available experimental data. The most favorable sites for electrophilic, nucleophilic attack or protonation were also identified using the noncovalent interaction method. [ABSTRACT FROM AUTHOR]

The first-principles calculations are carried out to explore more intensely on geometric, spectroscopic and electronic properties of M 20 (M = Cu, Ag, Au) species. Computed results show that the global minima of these clusters are compact, nearly spherical structures, while other low-lying isomers exhibit the oblate or probate shapes. For Cu 20 , we find it is in a C 3 symmetry form rather than the C s conformation as previously suggested. The vertical ionization energies for lower-lying isomers are also computed and assigned with respect to available experimental values. Although several isomers were predicted to be similar in energy content, the corresponding vibrational signatures are so distinctive that could be used as fingerprint signals to identify their geometrical forms. More importantly, the enhanced stability of these systems can be understood in terms of the phenomenological shell model. Computed results also recognize that the structures and properties of Ag 20 and Cu 20 clusters are similar and prefer compact structures, while Au 20 cluster exhibits structures different from with a tetrahedral form. [ABSTRACT FROM AUTHOR]

Geometric, energetic and electronic properties of Aun clusters, n = 2–20 are determined using DFT calculations (BB95/cc-pVTZ-PP). Global equilibrium structures were confirmed or found, and the growth mechanism was established. Au-clusters prefer 2D-geometries up to Au 11 and are generated from the lowest-lying isomer of the smaller size by adding an extra gold atom. Transition from an oblate form to a pyramid is observed at Au 17 . Au n containing 17–20 atoms favor tetrahedral evolution by adding atoms to the Frank-Kasper 16-vertex. Binding energy per atom, second-order difference of energy, and one-step fragmentation energy show that Au 6 and Au 20 have high thermodynamic stability. Their valence electrons of generate magic numbers that can be understood using the phenomenological shell model. Due to Jahn-Teller effect, Au 16 is characterized by oblate structure whereas the anion Au 16 -exhibits Frank-Kasper form. [ABSTRACT FROM AUTHOR]

Abstract: Properties of a series of MnX n with X=H, F, Cl, Br and n =1–4 are investigated using DFT, CCSD(T) and CASPT2 computations. The B3P86/6-311++G(3df,2d) method appears to be suitable for predicting their structures whose geometries and IR spectra are dependent on the charge state. While MnX2 are linear, MnX3 and MnX4 are characterized by high symmetry shape. The π-bonding type is observed for and . In halides, a different type of bonds is formed as p-orbitals of halogens can overlap with empty metal d-orbitals allowing a more effective electron transfer and high spin ground electronic states. Vibrational frequencies and basic energetic quantities are computed and compared with available experiments. Several previous thermochemical quantities are re-evaluated, and the heats of formation of Mn-compounds can be determined with reasonable accuracy using the B3LYP functional. However, while calculated ionization energies are in agreement with experiment, electron affinities are obtained with large deviations. [Copyright &y& Elsevier]

Density functional theory (DFT) calculations were carried out to explore the geometric, spectroscopic, and electronic properties of three magic silver clusters Agn (n = 8, 18, and 20) in detail. The computed results show that the global minima of these clusters are compact, near-spherical structures, while other low-lying isomers exhibit oblate or prolate shapes. Vertical ionization energies for the low-lying isomers were also computed and assigned with respect to available experimental values. Although several isomers were predicted to have similar energies, their electronic and vibrational signatures were quite distinctive, meaning that they could be used as fingerprint signals to distinguish between isomers. In addition, the electronic structures of these systems were explored using the phenomenological shell model. Calculations for the coinage metal clusters M20 (M = Cu, Ag, Au) indicated that the structures and properties of the Ag cluster are similar to those of the Cu cluster in that both Cu20 and Ag20 prefer a compact structure whereas Au20 prefers to adopt a tetrahedral form.Shell Orbitals of Ag8 Cluster [ABSTRACT FROM AUTHOR]