Showing papers on "Electronic structure published in 1970"

Electronic structure of palladium

Abstract: A detailed investigation of the electronic structure of palladium is presented in terms of two different band models: (1) ab initio calculations using the augmented-plane-wave method, and (2) calculations using the combined interpolation scheme augmented by inclusion of relativistic corrections. The width and position of the $d$-band complex are found to be particularly sensitive features of the electronic structure of palladium. A highly detailed density-of-states histogram, and estimates for the first and second derivatives of the density of states at the Fermi energy are derived. In addition, detailed comparisons are made with Fermi-surface-static susceptibility, and specific-heat experimental results. Estimates for the effects of manybody enhancements suggest that paramagnons raise the effective mass at the Fermi energy by only about 41%. Owing to the strong $s\ensuremath{-}d$ hybridization in palladium, the Fermi surface is made up almost entirely of $d$-like states. Because the Fermi energy in palladium falls near the strongly spin-orbit split levels at $X$ and $L$, spin quenching reduces the effective $g$ factor at the Fermi energy from 2 to about 1.65. This increases an estimate of the effective Stoner-enhancement factor from 10 to about 15.

Electronic Structure and Inversion Barrier of Ammonia

Abstract: Ab initio molecular orbital wavefunctions have been constructed for the planar and pyramidal conformations of ammonia in its ground electronic state. These solutions are very close to the Hartree–Fock limit and exhibit a lower total energy (ETequil = − 56.22191 hartree) than any other such calculations which have been carried out. The computed inversion barrier is 5.08 kcal/mole (exptl = 5.8 kcal/mole) and results almost solely from the differential mixing of d‐type polarization functions in the planar and pyramidal geometries. In contrast to the conclusions of much earlier work, the inversion barrier may be quantitatively obtained within the framework of the molecular orbital (Hartree–Fock) approximation. Other properties of ammonia that have been determined and discussed are: binding energy, heat of formation, correlation energy, dipole moment, population and energy component analysis, force constants, and the Walsh diagram.

Superconductivity: The Transition Temperature Peak Below Four Electrons per Atom

Abstract: It is shown that the superconducting transition temperature for compounds in seven different structure types exhibits a peak at about 3.7 to 3.9 valence electrons per atom.

Electronic Structures of Polymers Using the Tight‐Binding Approximation. II. Polyethylene and Polyglycine by the CNDO Method

Abstract: Formulas for the calculation of the electronic structure of polymers were derived by the tight‐binding approximation using the CNDO/2 method. This formalism was applied to the calculation of the electronic structure of polyethylene in the all‐trans conformation and polyglycine in the α‐helix form. For polyethylene, conformation analysis was carried out to obtain a fairly good agreement with the experimental results. The results of our conformation analysis were also in fair agreement with the calculation by the extended Huckel method which had already been published in this series of papers. The electronic structure of polyglycine was found to reflect the effect of the hydrogen bond formation in the α‐helix form.

Electronic Structures of Polymers Using the Tight‐Binding Approximation. I. Polyethylene by the Extended Hückel Method

Abstract: The formulas for the electronic structure of the polymer were given in terms of the extended Huckel method by the use of the tight‐binding approximation. Then, the electronic structure of polyethylene was calculated by means of these formulas to search for the most stable conformation. It was found that the fully extended all‐trans state was the state of minimum energy which was in harmony with the experiments. Moreover, the charge distributions on polyethylene with various conformations were calculated and compared with those of n‐propane, n‐pentane, and n‐heptane calculated by the extended Huckel method.

Localization in Disordered Materials: Existence of Mobility Edges

Abstract: Disordered materials electronic structure band states localization, examining mobility edges

Covalency and Electronic Structure of Cu2+ in ZnF2 by EPR

Abstract: With the aid of computer techniques, including a laboratory automation system, accurate computer simulation, and an accurate calculation method, the EPR spectrum of copper doped in zinc fluoride has been analyzed. The observed g values led by a new method to a determination of the coefficients of the Kramer's doublet. Copper hyperfine structure verified these values and fluorine transferred hyperfine structure gave a measure of covalency. The fractional orbital occupation showed predominantly σ bonding which is similar to other reported transition metal ions in ionic insulating crystals. Orbital reduction, though no doubt present, makes only an insignificant and undetectable contribution.

Electronic Transport in Alloys: Coherent-Potential Approximation

Abstract: The coherent-potential approximation, which has been successfully used to describe the electronic structure of a nondilute binary alloy ${A}_{x}{B}_{1\ensuremath{-}x}$, is reformulated in a diagrammatic way suitable for the calculation of more complicated transport coefficients. This approach is applied to the calculation of three elementary transport coefficients: the conductivity $\ensuremath{\sigma}$, the thermoelectric power $Q$, and the low-field Hall coefficient ${R}_{H}$. The appropriate response functions are evaluated for a simple cubic tight-binding model. The rigid-band limit is considered in detail, with emphasis on the role of critical points. As the random alloy potential increases, deviations from rigid-band behavior --- for example, Nordheim's rule --- become more pronounced for unexpectedly small scattering strengths. However, the usual relations among the transport coefficients, e.g., Mott's equation between $Q$ and $\ensuremath{\sigma}$, are maintained. The conductivity is no longer symmetrical with respect to electron and hole concentrations. Furthermore, the change in sign of $Q$ and ${R}_{H}$ may not occur when the band is half-full. Therefore, the identification of the carrier sign becomes ambiguous. For the model treated, numerical calculations are quite tractable. Examples are given which illustrate the behavior for a wide range of alloy parameters.

Electronic Structure of Titanium

Abstract: Augmented-plane-wave (APW) calculations of the electronic structure of titanium have been carried out. The resulting Fermi surface is compared to that predicted by the model of Altmann and Bradley based on cellular calculations and the APW model of Loucks for zirconium.

Electronic structure of thymine.

Abstract: The electronic structures of the ground and low‐lying excited states of thymine and the anions 1‐HT− and 3‐HT−, derived by removing a proton from nitrogen atom N3 and N1, respectively, have been described by all‐electron all‐integral LCAO–SCF calculations using Gaussian basis functions. In accord with experiment, we find the carbonyl bonds weakened in the anions relative to thymine because of a decrease in their overlap charge densities. On the other hand, our calculations and interpretation of the observed optical and ESR spectra suggest that both for T and 1‐HT− the lowest singlet and triplet π → π* states are very similar and localized in the region of the ethylenic bond of thymine.

Theoretical Analysis of the Electronic Structure and Molecular Properties of the Alkali Halides. V. Potassium Chloride and Lithium Bromide

Abstract: The results of recent self‐consistent field calculations on potassium chloride and lithium bromide are presented. Special emphasis is given to an analysis of molecular properties including nuclear quadrupole coupling constants, isotope shifts, spectroscopic constants, relativistic interactions, molecular force constants, and the electronic dipole moment.

The electronic structures of charge-transfer complexes: Application of the semiempirical SCF-MO-Cl method

Abstract: A method is developed to calculate the electronic structure of a molecular complex composed of a π-electron donor and a n-electron acceptor. The complex is treated as a single conjugated system of π-electrons, and its π-electron states are calculated by the semi-empirical SCF-MO-CI method within the n-electron approximation, by including all β terms. The method is applied to the TONE complexes of polycyclic aromatic hydrocarbons. It is shown that the absorption spectra of these complexes are well predicted by this method. Discussions are given on the mixing of the charge-transfer configurations and the locally-excited configurations.

Molecular modelling with spherical Gaussians

Abstract: A mathematical model of a molecule is proposed. The electronic structure is described using a molecular orbital wave function constructed from a small number of spherical Gaussians with optimized parameters. The models exhibit the desirable properties of numerical stability, objectivity and transferability. Results are given for CH4, C2H6, cyclo-propane, H2O, CH2O and C2H4. They can be given a chemical interpretation in terms of chemical bonds, lone pairs and atomic cusps.

Mössbauer Spectra of Iron Tetraphenylporphins

Abstract: Mossbauer spectra were measured for a series of the central iron in Fe(II)- and Fe(III) complexes of tetraphenylporphin. The electronic structure of the central iron in the complex was modified by the axial ligand field. The Mossbauer spectra assigned the most probable electronic configurations to various iron states in the iron porphins.

Pair Correlations and the Electronic Structure of Neon

Abstract: Using a variationally determined set of atomic orbitals, the validity of pair-correlation approximations is examined for the Ne atom. Summing the usual pair-correlation energies yields 100.5% of the correlation energy. By summing symmetry-adapted pair-correlation energies, 90.2% of the correlation energy is obtained. The complete second-order wave function which includes the Hartree-Fock configurations plus all singly and doubly excited configurations produces 88.6% of the correlation energy.