Showing papers on "Electronic structure published in 1976"

Nonlocal pseudopotential calculations for the electronic structure of eleven diamond and zinc-blende semiconductors

Abstract: An empirical nonlocal pseudopotential scheme is employed to calculate the electronic structure of eleven semiconductors: Si, Ge, $\ensuremath{\alpha}\ensuremath{-}\mathrm{Sn}$, GaP, GaAs, GaSb, InP, InAs, InSb, ZnSe, and CdTe. Band structures, reflectivity spectra, electronic densities of states, and valence charge densities are presented and compared to experimental results. Improved optical gaps, optical critical-point topologies, valence-band widths, and valence charge distributions are obtained as compared to previous local pseudopotential results.

Ab initio effective core potentials: Reduction of all-electron molecular structure calculations to calculations involving only valence electrons

Abstract: A formalism is developed for obtaining ab initio effective core potentials from numerical Hartree–Fock wavefunctions and such potentials are presented for C, N, O, F, Cl, Fe, Br, and I. The effective core potentials enable one to eliminate the core electrons and the associated orthogonality constraints from electronic structure calculations on atoms and molecules. The effective core potentials are angular momentum dependent, basis set independent, and stable against variational collapse of their eigenfunctions to core functions. They are derived from neutral atom wavefunctions using a pseudo‐orbital transformation which is motivated by considerations of the expected accuracy of their use and of basis set economy in molecular calculations. Then the accuracy is demonstrated by multiconfiguration Hartree–Fock calculations of potential energy curves for HF, HCl, HBr, HI, F2, Cl2, Br2, and I2 and one‐electron properties for HF and HBr. The differences between valence‐electron calculations employing the present...

Electronic structure of a metal-semiconductor interface

Abstract: The electronic structure of a jellium-Si interface is calculated using a jellium density corresponding to Al and self-consistent Si pseudopotentials. Local densities of states and charge densities are used to study states near the interface. At the Si surface, a high density of extra states is found in the energy range of the Si fundamental gap. These states are bulklike in jellium and decay into Si with a high concentration of charge in the dangling-bond free-surface-like Si state. Truly localized interface states are also found but at lower energies. The calculated barrier height is in excellent agreement with recent experimental results.

Electronic structure, spectra, and properties of 4:2-coordinated materials. I. Crystalline and amorphous SiO 2 and GeO 2

Abstract: A two-parameter tight-binding theory of the electronic structure of 4:2-coordinated materials is proposed. The parameters, a covalent and a polar energy, are fitted to the optical absorption spectra. The valence energy bands and density of states are calculated. In terms of these a consistent interpretation of all the observed photoemission and x-ray-emission spectra of ${\mathrm{SiO}}_{2}$ is obtained. The x-ray-absorption spectra are also analyzed. A bond-orbital approximation allows a simple calculation of the refractive index (or dielectric constant) of the various allotropic forms of silica and germania. Finally, the variation in total energy and charge distribution with local distortion is analyzed in order to study structural stability, elastic rigidity, and the effective charges (including dynamic contributions) which determine the piezoelectric constants and infrared absorption intensities.

Electronic spectra and electronic structure of TCNQ complexes.

Abstract: Electronic spectra of several TCNQ, complexes have been measured with single crystals by the transmission method. The assignment of electronic transitions are presented based on the electronic stru...

The electronic structure of solid surfaces

Abstract: We present a short review of the current status of electronic structure calculations for ordered solid surfaces. For the s--p bonded metal surfaces, emphasis is centered entirely on self-consistent field (SCF) calculations employing a local density approximation for exchange and correlation. For semiconductor surfaces both SCF and empirical tight-binding methods are discussed, while for transition metal surfaces, where no SCF calculations have been carried out, a number of different schemes for solving Schrodinger's equation at a surface are reviewed that use plausible but not self-consistent forms for the surface potential. Finally, calculations for chemisorbed systems are briefly covered, with emphasis on ordered monolayers on semiconductor and transition metal surfaces. (AIP)

Electronic Structure of Amorphous Semiconductors

Abstract: The Fermi energy as a function of electronic density and temperature is calculated for a defect level in which the effective intrasite electronic correlation energy is negative. It is found that the Fermi level lies below the energy of the highest-filled quasiparticle state, even at $T=0$, a result which favors $p$-type conduction. Futhermore, the Fermi energy varies only very slowly with electronic density and temperature, and thus is effectively pinned.

Electronic states of KrF

Abstract: We report ab initio calculations on the electronic states of KrF arising from the Kr+F, Kr++F−, and Kr*+F separated atom limits. We conclude, in agreement with earlier assignments, that the observed laser transition is C (1/2) ‐X (1/2) (5.15 eV calculated, 5.00 eV observed). The calculated lifetime of the C (1/2) state is 6.5 ns. The ionic 2Π state was found to lie close to the ionic 2Σ+ state.

The electronic structure of the uranyl ion: Part I. The electronic spectrum of Cs2UO2Cl4

Abstract: The low-temperature single-crystal optical absorption spectrum of Cs2UO2Cl4 is reported in six different polarizations Measurements have also been made on the 18O compound Zeeman-effect measureme

Principles of Mössbauer Spectroscopy

Abstract: 1 The Mossbauer Effect.- 2 Hyperfine Interactions.- 3 Molecular Structure.- 4 Electronic Structure and Bonding: Diamagnetic Compounds.- 5 Electronic Structure and Bonding: Paramagnetic Compounds.- 6 Dynamic Effects.- 7 Oxides and Related Systems.- 8 Alloys and Intermetallic Compounds.- 9 Analytical Applications.- 10 Impurity and Decay After-effect Studies.- 11 Biological Systems.- Observed Mossbauer Resonances.

The electronic structure of NO2. II. The ? 2B2← ? 2A1 and ? 2B1←? 2A1 absorption systems

Abstract: The results of an accurate ab initio study of the electronic structure of NO2 have been applied to an analysis of the two important visible and near infrared absorption systems of this molecule. The long wavelength absorption (λ≳6000 A) arises from an ? 2B2←? 2A1 transition. A theoretical absorption spectrum that is generated from the C2V ab initio potential surfaces of these two states qualitatively reproduces most of the features of an experimental low resolution absorption spectrum between 9000 and 6000 A. The (0–0) band of the transition is predicted to be several times less intense than nearby hot bands even at temperatures as low as 300 K. The computed ? 2B2 spectroscopic parameters are Te=1.18 eV, Re=1.26 A, ϑe=102°, ω1=1461 cm−1, ω2=739 cm−1, and μ=0.46 D. There is a marked difference between experimentally determined ? 2B2 rotational constants and those deduced from the ab initio equilibrium geometry; this datum adds to the rapidly increasing evidence for strong vibronic coupling of the ? 2B2 sta...

Optical properties, phonons and electronic structure of iron pyrite (FeS2)

Abstract: The reflectivity spectrum has been measured for photon energies between 0.03 eV and 12 eV and the optical transmission between 0.03 eV and the absorption edge at 0.95 eV. The real and imaginary part of the dielectric function have been calculated using a Kramers-Kronig analysis and an energy level scheme has been derived. All phonon modes expected by group theoretical analysis have been observed.

The electronic structure of molecules by a many‐body approach. I. Ionization potentials and one‐electron properties of benzene

Abstract: The ionization potentials of benzene are studied by an ab initio many‐body approach which includes the effects of electron correlation and reorganization beyond the one‐particle approximation. The calculations confirm the assignment of the photoelectron spectrum experimentally proposed by Jonsson and Lindholm: 1e1g(π), 2e2g, 1a2u(π), 2e1u, 1b2u, 1b1u, 2a1g, 1e2g in order of increasing binding energy. To definitely establish the ordering of the ionization potentials in the second band, which has been very controversial, the corresponding vibrational structure has been calculated. A number of one‐electron properties are calculated in the one‐particle approximation and compared to experimental work and other theoretical calculations.

Synchrotron radiation studies of electronic structure and surface chemistry of GaAs, GaSb, and InP

Abstract: The oxidation properties of GaAs(110), GaSb(110), and InP(110) have been studied with the photoemission technique using synchrotron radiation. One part of the work consisted of an investigation of the chemical shifts in the core levels upon adsorption of oxygen in submonolayer quantities. For GaAs and InP, oxygen removed electrons preferentially from the surface column V elements (As and P), leaving the column III elements (Ga and In) unaffected; whereas, for GaSb, both constitutents were involved in the oxidation suggesting a breaking of bonds between the surface atoms and the rest of the crystal. The second part of the study consisted of a careful investigation of the Fermi level (Ef) pinning in the GaAs(110) surface. Three different samples and many cleaves were studied. For one sample, Ef was always at the bulk position. On the other two crystals, both pinned and unpinned cases were found on various cleaves. The unpinned samples had sharp electron distribution curves (EDC’s), while the pinned samples ...

Comprehensive study of satellite structure in the photoelectron spectra of transition metal compounds

Abstract: A wide variety of different transition metal compounds have been studied for their satellite structure found in photoelectron spectra, with specific emphasis on the 2p shell of the first-row transition metals. In particular, data on halides and cyanide complexes are presented. Results on second- and third-row transition metal compounds are also discussed. The relative roles of electron shake-up and multiplet splitting for producing the satellite structure are evaluated. The behavior of the satellite structure is generalized as a function of metal ion and ligand and the energy spacing of the metal and ligand orbitals. It is ascertained that the large, well-defined satellite peaks are due to electron shake-up involving excitation of electrons from a ligand to a metal orbital. (auth)

The effect of the surface structure of Pt on its electronic properties and the adsorption of CO, O2, and H2: A comparison of Pt(100) – (5×20) and Pt(100) – (1×1)

Abstract: We describe studies of the Pt(100) – (1×1) and Pt(100) – (5×20) surfaces with LEED, UPS, AES, and flash desorption spectroscopy. The clean Pt(100) – (1×1) surface is prepared by adsorbing CO, then reacting it off with oxygen ions in the form of CO2. The clean (1×1) surface formed is metastable, converting back to the (5×20) surface at 125 °C. This and other evidence leads us to the conclusion that the (5×20) surface is the clean equilibrium structure. The electronic structure of the (1×1) surface is characterized by a surface state or resonance 0.25 eV below the Fermi level, which is not observed on the (5×20) surface. Although O2 and H2 do not chemisorb at room temperature for exposures less than 102 equivalent monolayers on the (5×20) surface, the (1×1) surface readily chemisorbs O2 and H2. It is suggested that the structure sensitivity of the O2 and H2 chemisorption observed may be due to the corresponding change in surface electronic structure. CO adsorbs on both the (5×20) and (1×1) surfaces. At 0.5 ...

Electronic structure of Sm monochalcogenides

Abstract: The optical reflectivity of single crystals of semiconducting SmS, SmSe, and SmTe as well as of the metallic, high-pressure phase of SmS has been investigated in the photon energy range between 0.03 and 12 eV, for metallic SmS also between 4.2 and 300 K. The dielectric functions have been derived by means of a Kramers-Kronig analysis and been interpreted by interband and intraband transitions. In addition, semiconducting evaporated films of SmS have been prepared and the absorption in function of temperature (4.2-300 K) and pressure (0-1.5 kbar) has been investigated. It can be shown that the electronic structure of the semiconducting Sm monochalcognides can be obtained from the corresponding one of the Eu monochalcogenides by a simple uniform shift in the energy of the $4f$ electronic state. Valence fluctuations in single crystalline, metallic SmS are present to a much lower degree than assumed so far.

A theoretical study of the electronic structure of ferrocene and ferricinium: Application to Mössbauer isomer shifts, ionization potentials, and conformation

Abstract: Self‐consistent field wavefunctions have been obtained for ferrocene and several low‐lying states of the ferricinium ion using extended basis sets of contracted Gaussian functions. In agreement with the near minimal basis set results of Coutiere e t a l., the electronic structure is found to change very considerably when ferricinium is formed by removing an electron from an Fe d molecular orbital of ferrocene. The ionicity of Fe, as determined by a Mulliken gross population analysis, is found to be +1.47 for the ion and +1.39 for ferrocene. The difference is less than 0.1 electrons, while a value close to one would have been expected. The major contribution to the change in structure comes from a greatly increased covalency of the ligand orbitals of e 1g symmetry in the ion. The change is shown to be responsible for the small differences found between the isomer shifts, and thus electron densities at the Fe nucleus, in ferrocene and ferricinium salts. Direct contributions from Fe 4s electrons are found to account for about half of the 0.93a −3 0 difference in the electron density. A value of the change in nuclear radius, δR/R=−4.4×10−4, is estimated from the computed densities. Computed values of the six lowest ionization potentials of ferrocene are compared with photoelectron spectra, and symmetry assignments of the ionic levels are made. The average error of the computed ionization potentials is 0.5 eV, giving confidence to these assignments. For the states considered, wavefunctions have been obtained for both the eclipsed and staggered conformations of the C5H5 rings. Both absolute and relative total energies are found to be essentially the same for either conformation.

Electronic states of substoichiometric compounds and application to palladium hydride

Abstract: Results of a CPA calculation of the density of states of Pd-H for H/Pd between 0 and 1 are reported The superconductivity of such compounds is discussed and a recent theory of Papaconstantopoulos and Klein is found to be reasonable 15 references

Electronic band structures and x-ray photoelectron spectra of ZrC, HfC, and TaC

Abstract: The band structures and densities of states (DOSs) of ZrC, HfC, and TaC were calculated by the augmented-plane-wave method, and the x-ray photoelectron spectra of valence bands of these compounds were observed. The theoretical energy distribution curves (EDCs) were in good agreement with the experimental EDCs. These band structures resemble each other and also those of TiC obtained by our previous work. This fact suggests that the rigid-band model is applicable to the transition-metal carbides with the rock-salt structure. Their DOSs are divided into three parts. Peak I derived from the $\mathrm{C} 2s$ state is isolated from the higher valence-band peak II arising from the $\mathrm{C} 2p$ and the valence electrons of the metal atom. Peak III derived from the $d$ and $s$ states of the metal atom is separated by the Fermi level from peak II. The Fermi level lies at the minimum point of the DOS for the group IV carbides, but for TaC it lies at a relatively large DOS point. The DOS at the Fermi level of ZrC, HfC, and TaC are 0.18, 0.16, and 0.65 electrons/(eV primitive cell), respectively. The characteristic mutual differences among these compounds are a stronger localization of $d$ electrons in ZrC and HfC compared with TiC and an enhancement of the photoelectron spectrum intensity of TaC around the Fermi level.

The effect of pressure on the physics and chemistry of potassium

Abstract: The equation of state and electronic structure of body-centered cubic potassium are investigated theoretically by the quantum-mechanical SAPW method. The results predict a series of pressure-induced electronic phase changes brought about by the sequential filling of initially unoccupied d-like electronic states. In addition to the discontinuous density changes that accompany these phase transitions, the presence of the d-like bands makes potassium extremely compressible. At pressures as low as 500 kb (0°K), the ionic radius of potassium becomes compatible with that of iron and its electronic structure becomes like that of a typical transition metal. These properties should greatly enhance the miscibility of potassium in iron or iron-sulfide melts.

Theoretical determination of the electronic structure and the spatial arrangement of ferrous iron in deoxygenated sperm whale myoglobin and human hemoglobin from Mössbauer experiments

Abstract: The electronic term scheme of ferrous iron in sperm whale myoglobin (Mb) and human hemoglobin (HbA) is evaluated by a Hamiltonian which involves the Coulomb repulsion of the 3d electrons, their interaction with the tetragonally arranged ligands, a small rhombic perturbation of the C4v point symmetry, and spin–orbit coupling. The temperature dependence of the quadrupole splitting in both compounds was measured and the adjustable parameters of the theory were determined by a least squares fit to the experimental results. It was found that the five lowest singlets mainly descend from the rhombic‐split 5E term. The low‐lying 1A1, 5B2, and 3E levels contribute to the low‐energy spectrum too. The least squares fit yields a different term scheme for Mb and HbA. In both compounds, however, the spin–orbit coupling constant λ and the covalency factor α2 of the quadrupole interaction prove to be λ?69 cm−1 and α2?0.89. The calculated electric field gradient agrees with the single crystal experiment on Mb at 77 K. Owi...

Effects of secondary ligands on the electronic structure of uranyls

Abstract: The effects of secondary ligands on the electronic structure of uranyl, UO2 ++, are investigated in a perturbing point ion model, making use of the relativistic Dirac–Slater molecular orbital (MO) approach. Variation of ’’crystal‐field splittings’’ with primary U–O bond length is explored; relaxation of the uranyl MO’s is taken into account by self‐consistent iterations. The theoretical splittings are found to agree rather well with the x‐ray photoemission spectroscopy (XPS) data of Veal et al. Comparison is made with optical data and reasons are given for the poor agreement.

Electronic Structure of Ni-Mn and Ni-Fe Alloys

Abstract: The electronic structures of ferromagnetic Ni-Mn and Ni-Fe alloys are investigated theoretically. The Hartree-Fock calculation combined with the coherent potential approximation is shown to give two magnetic states for Mn and Fe atoms in Ni-Mn and Ni-Fe alloys, respectively. By introducing the ternary alloy picture in which Mn(Fe) atoms having antiparallel moments to the bulk magnetization are distinguished from Mn(Fe) atoms having parallel moments for a given Ni-Mn(Ni-Fe) alloy, the possibility of the coexistence of the two magnetic states is shown by an energy consideration. On the basis of the results obtained by this calculation, various magnetic properties are discussed.