Thorium compounds with non-metals: Electronic structure, chemical bond, and physicochemical properties

The current state of research on the nature of the chemical bond and the physicochemical properties of binary Th-X (X = H, B, C, N, O, P, S, As, Se, Sb) and ternary (carbonitrides, thorates, and silicates) thorium compounds by modern ab initio methods of the band structure theory is reviewed. The possibilities of the ab initio band structure methods in describing the structural states, phase stability, elasticity characteristics, X-ray emission, absorption, and photoelectron spectra of thorium-containing systems are discussed.     

Electronic structure and chemical bonding in lanthanide titanates

Institute of Chemistry, Ural Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 6, pp. 25–31, November–December, 1990.     

Electronic structure, chemical bonding, and spin polarization in ferromagnetic MnAl

The electronic structure of ferromagnetic τ-MnAl has been calculated using density-functional techniques (TB-LMTO-ASA, FLAPW) and quantum-chemically analyzed by means of the crystal orbital Hamilton population tool. While all observable quantities are in good agreement with experiment, the tetragonal structure of ferromagnetic MnAl is interpreted to arise from a nonmagnetic cubic structure by two subsequent steps, namely (a) an electronic distortion due to spin polarization followed by (b) a structural distortion into the tetragonal system. The various strengths of interatomic bonding have been calculated in order to elucidate the competition between electronic and structural distortion.     

Electronic structure and chemical bonding in bismuth sesquioxide polymorphs

The electronic structure of the α-Bi₂O₃, Β-Bi₂O₃, and γ-Bi₂O₃ phases was investigated by the ab initio self-consistent LMTO method in a tight binding approximation and by the semiempirical Hückel method. The total and partial densities of states and Mulliken overlap populations were obtained. The stability of bismuth oxide polymorphs is discussed based on the results of the total energy calculations for crystals. An analysis of chemical bonding shows that the Bi-O interaction plays the leading role. The Bi-Bi metallic bond is absent. Mechanisms of oxygen ion migration and possible stabilization of the structure of the superionic conductor δ-Bi₂O₃ are discussed.     

Electronic structure and chemical bonding in nonstoichiometric zirconium nitrides

X-ray emission spectra were taken and band calculations using the Green function LMTO method and cluster calculations using the discrete variational X method were carried out for the electronic structure and chemical bonding parameters for nonstoichiometric zirconium nitrides containing metallic and metalloid vacancies. The existence of structural defects leads to a redistribution of the occupancies of the major sub-bands of the nitride valence spectrum and the formation of a new group of states between the p-d- and d-like bands of ZrN_1.0.Institute of Chemistry, Urals Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 5, pp. 82–89, September–October, 1989.     

Electronic structure and chemical bonding in Ba-Cu-O layer systems

The cluster method of discrete variation was used to study compounds containing chains of plane-coordinated copper ions separating oxygen-copper planes. We also examined real YBa₂Cu₃O₇ and hypothetical MBa₃Cu₄O₉ systems (M is a tetravalent metal ion). A study was carried out on the transformation of the valence band and structure of the molecular orbitals in the Fermi level in going from YBa₂Cu₃O₇ to MBa₃Cu₄O₉. The chemical bonding was analyzed and the role of the interchain interaction in the bonding of the copper and oxygen atoms in different crystallographic positions was determined.Institute of Chemistry, Urals Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 5, pp. 17–20, September–October, 1989.     

Electronic structure,Fermi surface,and chemical bonding in new layered oxyselenide: HgCuSeO

A full-potential FLAPW-GGA method is used to study for the first time the electronic structure of new layered HgCuSeO oxyselenide with a tetragonal structure. The band structure, density of electron states, Fermi surface, and effective atomic charges are obtained and analyzed; the coefficients of low-temperature heat capacity and paramagnetic Pauli susceptibility are estimated. It is shown that the new layered HgCuSeO phase can be characterized as non-magnetic ionic metal.     

Uranyl heteropolyoxometalate: synthesis, structure, and spectroscopic properties

A novel uranium heteropolyoxometalate, [H(3)O](4)[Ni(H(2)O)(3)](4){Ni[(UO(2))(PO(3)C(6)H(4)CO(2))](3)(PO(4)H)}(4)·2.72H(2)O, has been prepared under mild hydrothermal conditions using the diethyl(2-ethoxycarbonylphenyl)phosphonate ligand and in situ ligand synthesis of the HPO(4)(2-) anion. The cluster is derived from a common UO(7), pentagonal bipyramid and is constructed by employing nickel(II) metal ions as linkers. The 3d-5f heteropolyoxometalate core incorporates 12 classical pentagonal uranyl groups and four Ni(2+) octahedral units.     

Electronic structure, chemical bonding, and geometry of pure and Sr-doped CaCO3

The electronic structure, chemical bonding, geometry, and effects produced by Sr-doping in CaCO(3) have been studied on the basis of density-functional theory using the VASP simulation package and molecular-orbital theory utilizing the CLUSTERD computer code. Two calcium carbonate structures which occur naturally in anhydrous crystalline forms, calcite and aragonite, were considered in the present investigation. The obtained diagrams of density of states show similar patterns for both materials. The spatial structures are computed and analyzed in comparison to the available experimental data. The electronic properties and atomic displacements because of the trace element Sr-incorporation are discussed in a comparative manner for the two crystalline structures.     

Electronic structure and chemical bonding of δ-Bi2O3

The band structure of the fluorite-type δ-Bi₂O₃ was calculated by the linear LMTO methods in the approximation of overlapping atomic spheres using the basis set of orthogonal orbitals (LMTO-ASA) and by the full-potential LMTO method (LMTO-FP) for two vacancy orientations over a wide range of oxygen concentrations. The calculated parameters of chemical bonds—the binding energy E_bin and the pressure of the electron-nuclear system—show that the most stable compound is that with two vacancies per unit cell, oriented predominantly along the (111) direction. The hybrid Bi−O bonds are weak, and mostly the Bi−Bi bonds are responsible for the structural stabilization of δ-Bi₂O₃. The mechanism of the formation of a semiconductor gap in the band structure of δ-Bi₂O₃ is discussed. Institute of Solid State Chemistry, Ural Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 48–58, January–February, 1996. Translated by I. Izvekova     

Electronic structure of CO--an exercise in modern chemical bonding theory

This paper discusses recent progress that has been made in the understanding of the electronic structure and bonding situation of carbon monoxide which was analyzed using modern quantum chemical methods. The new results are compared with standard models of chemical bonding. The electronic charge distribution and the dipole moment, the nature of the HOMO and the bond dissociation energy are discussed in detail.     

A computational study of the electronic structure, bonding, and spectral properties of tripodal tetraamine Co(III) carbonate complexes

Density functional calculations have been carried out on the experimentally characterized Co(III) [Co(N4)(O2CO)]+ carbonate complexes containing a tripodal tetraamine ligand (N4 = tpa, Metpa, Me2tpa, Me3tpa, pmea, pmap, tepa) and also the model [Co(NH3)4(O2CO)]+ system. Calculations on the model species, performed using both gas-phase and solvent-corrected procedures, have revealed that the inclusion of a condensed-phase environment is necessary to obtain generally satisfactory results for the structural and bonding properties in these systems. Using the solvent-corrected approach, the observed trends in structural parameters for the metal-ligand bonds, 59Co chemical shifts, and changes in visible absorption wavelengths have been satisfactorily reproduced for the [Co(N4)(O2CO)]+ complexes. A time-dependent density functional analysis of the electronic excitations indicates that the overall composition and character of the relevant (d-d) transitions remain similar throughout the series, indicating that the changes in the Co-N interactions, associated with the structural variations occurring as the N-donor ligand identity and size change, appear most likely responsible for the particular spectroscopic features displayed by these species. These observations are further supported by molecular orbital and energy decomposition analyses. The results from the present calculations confirm recent findings that the inclusion of a treatment for solvent effects plays a critical role in the computational modelling of coordination complexes involving mixed (anionic and neutral) ligands.     

Actinide metals and intermetallic compounds: Electronic structure and magnetic properties

Cohesive properties are calculated for the AnIr₂ and AnRh₃ series of intermetallic systems. The positive and negative deviations from Vegard's law found in both series are emphasized. The development of magnetism and 5f localization as a function of increasing actinide atomic number is studied in detail for the two classes of compounds. A relativistic formulation of the Stoner criterion for ferromagnetism is presented and applied to a number of actinide systems. Finally the ferromagnetism of UFe₂, NpFe₂ and PuFe₂ is treated theoretically. For these intermetallic compounds it is found necessary to implement all three Hund's rules into the calculations, before agreement with experiment is obtained.