Showing papers on "Electronic band structure published in 1980"

The Recursive Solution of the Schrodinger Equation

Abstract: Publisher Summary The chapter presents a study on the recursive solution of the Schrodinger equation. The local environment approach to the electronic structure of solids requires an alternative to band theory for solving the Schrodinger equation. In the limit of weak interaction between electrons and atoms, for example in simple metals, the electronic structure is determined by the long-range periodicity of the atomic potentials. Band theory exploits this aspect of the physics to express electronic properties of the solid as a coherent superposition of the electronic properties of all the atoms. When the electrons interact strongly with the atoms, this picture breaks down and properties no longer depend on long-range periodicity, but rather on only the first few shells of neighbors of each atom. The d electrons in transition metals are prime examples of this regime. While band theory is still a valid, formal solution to the Schrodinger equation, the physics is better understood by means of a solution that explicitly accounts for the role of local environment. This chapter presents a discussion on such a method of solution of the Schrodinger equation. The recursive solution of the Schrodinger equation is well adapted to the digital computer. The chapter is organized in order of sophistication of the applications. The elementary part finishes with Green functions. The topics apply to particular kinds of calculations, such as local density of states, energy differences, and photocurrents.

Angle-resolved photoemission determination of the band structure and multielectron excitations in Ni

Abstract: Angle-resolved photoelectron spectroscopy utilizing polarized synchrotron radiation has been used to determine the electronic energy states of Ni. The dispersion of the $\mathrm{sp}$ band and all of the high-symmetry points in the Ni band structure have been determined. The linewidth in the spectra from the various high-symmetry points is used to estimate the magnitude of the exchange splitting throughout the $d$ band. The measured $d$-band width is 30% smaller than predicted by calculations whereas the $\mathrm{sp}$-band width agrees within 10%. Several peaks in the photoelectron spectra which appear between 6 and 27 eV below the Fermi energy are shown to originate from multielectron excitations.

The crystal structure of IV-VI compounds. I. Classification and description

Abstract: It is shown that the crystal structures of the binary IV-VI compounds can be classified by parameters derived from a Pauli-force model potential, which has previously been used successfully for the octet and suboctet materials (ANBP-N with P=8 and 2

Electronic structure of magnetic impurities calculated from first principles

Abstract: The electronic structure of magnetic $3d$ impurities in Cu and Ag is calculated self-consistently from first principles. Using the density functional theory the exchange and correlation is treated in the local spin-density approximation of von Barth and Hedin. Our method is based on the Kohn-Korringa-Rostocker Green's-function method and the impurity is described by a single perturbed muffin-tin potential in an otherwise periodic lattice. We give results for the local density of states, the magnetic moments, and the phase shifts at the Fermi energy for the $3d$ impurities in Cu and Ag. Our results are in qualitative agreement with the Anderson model, however modifications due to the host band structure are important, especially for Mn and Fe in Cu. For all cases studied, the exchange integral $I$ lies between 0.65 and 0.8 eV.

Angle-resolved photoemission studies of the band structure of Ti Se 2 and Ti S 2

Abstract: The electronic structure of high-quality Ti${\mathrm{Se}}_{2}$ and Ti${\mathrm{S}}_{2}$ crystals has been investigated using angle-resolved photoemission with HeI, HeII, and NeI resonance radiation. Results compare well with recent self-consistent energy-band calculations although differences occur which may be due to the three- rather than two-dimensional nature of specific bands. Occupied $d$ states at the zone edge are observed in both materials. A small overlap with the $\frac{s}{p}$ valence band at $\ensuremath{\Gamma}$ is observed in the case of Ti${\mathrm{Se}}_{2}$ in approximate agreement with other workers. Ti${\mathrm{S}}_{2}$ appears to be a defect semiconductor with a band gap of 0.3 \ifmmode\pm\else\textpm\fi{} 0.2 eV.

Electronic structure of La monopnictides

Abstract: The one-electron energy band structure for YSb and a series of La pnictides, i.e. LaN, LaP, LaAs and LaSb, which attract particular interest as a proper reference material for the study of various anomalous properties of Ce pnictides, is calculated self-consistently by an APW method with the local-spin-density approximation exchange potential. In all La pnictides, narrow 4f bands lie a few eV above the Fermi energy, and distort the valence band appreciably. The calculated bands are metallic for all pnictides, though the density of states at the Fermi energy for LaN is far smaller than for other pnictides, in qualitative agreement with the observed transition from a semiconductor to a metal through the La pnictides. The calculated density of states at the Fermi energy for all pnictides except LaN agrees quantitatively well with the experimental result. The calculated valence band density of states for each La pnictide accounts qualitatively well for the valence band part of the recent experimental XPS spectrum of the corresponding Ce pnictide.

Self-consistent linearized augmented-plane-wave study of the electronic structure and superconductivity of fcc lanthanum under pressure

Abstract: We report the results of a linearized augmented-plane-wave calculation of the electronic structure of fcc La at three lattice constants corresponding to ambient pressure, 50, and 120 kbars. The Kohn-Sham-Gaspar approximation for exchange and correlation is used and the potential is allowed a fully non-muffin-tin form. The f bands lie approx.2--2.5 eV above the Fermi level and are approx.1 eV wide, resulting in a very small (0.05 electrons) localized f occupation. Under pressure the f bands rise and broaden appreciably, resulting in only a slight increase in f occupation. The rigid-muffin-tin approximation for the electron-phonon interaction lambda overestimates the superconducting transition temperature T/sub c/ by 40%, but we find that the drastic increase in T/sub c/ under pressure can be attributed primarily to changes in the electronic stiffness eta. Structural transitions which occur at 25 and 53 kbars may be related to changes in Fermi-surface topology which we find to occur approximately at these pressures.

The electronic emission spectrum of triatomic hydrogen. II. The perpendicular bands near 7100 Å

Abstract: The strongest emission bands of H3 and D3 near 7100 A are shown to be bands even though of a somewhat unusual structure. Because of the large width of the lines (the same as those of the 5600 A bands) the only method of analysis is by model bands whose parameters are changed until the best fit between observed and calculated spectrum is obtained. As expected on the basics of the line width the lower state is found to be identical with that of the 5600 A band, i.e., 2s2A1′, while the upper state is 3p2E′. The band structure of a band depends strongly on the value of ζ, the electronic angular momentum. When as in the present case ζ is close to 1, pseudo-branches with a constant N – K form the most characteristic features of the band. The ζ value determined here for the 3p2E′ state of D3 is 0.8775 which is very close to the ab initio value of King and Morokuma after the latter has been corrected for quenching by the zero-point vibration as a result of Jahn–Teller interaction. In addition the band structure s...

Electronic energy-band structure of the calcium fluoride crystal

Abstract: A self-consistent-field calculation for the electronic energy-band structure of the Ca${\mathrm{F}}_{2}$ crystal has been performed by using the method of linear combinations of atomic orbitals. The basis set consists of 90 Bloch sums formed by atomic wave functions of Ca and F as well as single-Gaussian orbitals. The valence-band states are composed chiefly of F $2p$ orbitals with both the upper and lower edges at the $X$ point. The x-ray structure factors are obtained from the valence-band wave functions and are compared with the observed values. The conduction states in the energy range of 1-3 eV above the threshold have substantial admixture of the Ca $3d$ orbitals, resulting in high density of states in that region. The calculated band gap is 10.0 eV which is somewhat smaller than the experimental value estimated from the reflectance spectra. Comparison of the calculated joint density of states with experimental optical data is discussed.

A Unified Theory of Magnetism in Narrow Band Electron Systems

Abstract: A unified description is given for magnetism of narrow band electron systems on the basis of a functional integral formalism within the static approximation. A method is developed to calculate the free energy functional from a given band structure and its closed form expression is given for arbitrary amplitudes of the spin and charge density fluctuations, correponding to arbitrary strength of the electron-electron interaction. This expression is shown to lead to essentially correct results in both the weak and strong coupling limits. The metal-insulator (Mott) transition and related magnetic properties for the case of half-filled band and the magnetism of metals in the case of non-integral occupation number per atom are discussed with a numerical example for a tight-binding band in a simple cubic lattice.

Experimental determination of bulk energy band dispersions.

Abstract: This paper reviews the methods of determining energy band dispersions in a tutorial way. Angle resolved photoemission techniques are applied that take advantage of a polarized tunable light source like synchrotron radiation. Various approximations (including exact methods) are described that have been made to obtain energy band dispersions (E vs k) directly from experiment, using a simple three-step model of photoemission. Apart from the energy E and the momentum k, there are symmetry quantum numbers of electron states in a crystal, which can be determined by using polarization selection rules. Examples are discussed for various methods and materials. In conclusion, the theoretical and practical limits of the band structure concept are considered.

Photoelectrochemical and solid‐state properties of LuRhO3

Abstract: Rare‐earth rhodates of the distorted perovskite structure are semiconductors with a band gap of 2.2 eV. They may be doped either n or p type. The oxides are stable against photodecomposition at the potential for hydrogen evolution. With ceramic p‐type LuRhO3 as the cathode and n‐type TiO2 as the anode of an electrolytic cell sufficient photopotential is developed both to photoelectrolyze water in sunlight with no externally applied potential and to generate power simultaneously. As synthesized, LuRhO3 is p type as determined by thermoelectric power measurements, but may be doped n type by the introduction of Th+4 during synthesis. Electrical resistivity data show that this oxide passes through compensation as the doping level increases, the activation energy at compensation being one‐half the optical band gap. The concentration of donor and acceptor impurities was determined by magnetic susceptibility to be in the vicinity of 1% for all samples. From these data, an estimate of 2.5 cm2/V sec can be made for the mobility of holes and 1 cm2/V sec for the mobility of electrons. Unlike most n‐type oxides reported, LuRhO3 possesses deep lying impurity levels and surface capacitance is far from Mott‐Schottky behavior. We have developed a theory of surface capacitance for deep levels, and the data agree well with theory. It is interesting to note that the Fermi level of LuRhO3 is pinned to the electrolyte at the same potential independent of whether the oxide is p or n type.

Band structure model and electrostatic effects in third and fourth stages of graphite acceptor compounds

Abstract: 2014 The model of independent graphite subsystems is extended to describe the electronic states in stages 3 and 4 of GAC. The electrostatic effects related to the nonequivalence of the internal and external graphite layers are proved to induce a non uniform charge distribution in the system, and also to modify drastically the band structure. Interband optical transitions are analysed within this model. With a charge transfer coefficient comparable to the value obtained for lowest stages of GAC, the expected energies of the intervalence transitions are close to the energies of the reflectivity structures observed experimentally. J. Physique 41 (1980) 667-676 JUILLET 1980,

Electron Lattice Interaction and Lattice Instability of 1T-TiSe2

Abstract: Lattice instability of 1 T -TiSe 2 is studied on the basis of the electronic band structure of this compound obtained by a tight-binding fit to the Zunger and Freeman's band. The electronic susceptibility, for which the wave number dependence of electron-lattice matrix elements is taken into account, is calculated for several phonon modes of wave vectors at the M and L points in the Brillouin zone. The results are discussed in connection with the lattice instability.

Combined LEED, AES, and work function studies during the formation of Ge : GaAs(110) heterostructures

Abstract: On clean, cleaved GaAs(110) surfaces Ge was deposited by MBE up to a thickness of 100 monolayers at different growth temperatures. At the interface Ge reacts with the GaAs. As measured by AES (0.65±0.25) monolayers of arsenic are dissolved and mainly segregated at the surface of the growing film. At a growth temperature of 295 °C the interface is abrupt, but broadened by diffusion for growth at 395 °C. With Ge films thicker than 5 monolayers a well developed 3×1 LEED pattern is observed which converts to a 2×1 pattern during an anneal above 400 °C. The LEED patterns are interpreted by surface segregation of GeAs2 and GeAs layers, respectively, one to two monolayers thick. The observed increase of the work function in the submonolayer coverage range is explained by band bending due to chemisorption induced surface states at Ess−Ev=0.89 eV and with a charge transfer of −(0.2±0.1) e0 per Ge atom. Therefore it is concluded that the Ge atoms bond to As atoms in the initial growth stage. The band scheme of the heterostructure is discussed, and the conduction band discontinuity of the Ge:GaAs(110) heterstructure is estimated as ΔEc?0.12) eV.

Column III and V elements on GaAs (110): Bonding and adatom‐adatom interaction

Abstract: Column V elements adsorbed on GaAs (110) exhibit strikingly different behavior than adsorbed column III elements in terms of the overlayers bonding to the semiconductor, the effect on the semiconductor surface lattice, and long‐range order. A strong interaction between adatoms is found with submonolayer coverings of column III metals which leads to the formation of flat raftlike metallic patches. Unlike the column III metals, Sb adsorption produces large changes in the electronic states and atomic arrangement of the semiconductor surface lattice. An elementary view of the factors responsible for the different characteristics and effects of these overlayers on GaAs (110) is given, but its extension to other adatoms is shown to be limited. These results have strong relevance to current theoretical models of Al and Ga overlayers on GaAs (110), as well as to molecular beam epitaxy and Schottky barrier formation.

Electronic structure and magnetism of CuNi coherent modulated structures

Abstract: The electronic and magnetic properties of a coherent modulated structure consisting of three atomic layers each of Cu and Ni perpendicular to (111) were determined from ab initio self-consistent spin-polarized energy-band calculations. We predict a susbtantial reduction in spin magnetization and contact hyperfine fields H/sub n/ at the Ni layers (in contrast with enhancements reported earlier from ferromagnetic resonance measurements), charge (0.1e/sup -/) and spin (approx.0.01..mu../sub B/) transfer to the Cu sites, and large H/sub n/ at the Cu nuclei.

Electronic structure of the diamond (111) 1×1 surface: Valence‐band structure, band bending, and band gap states

Abstract: Photoemission, LEED, and AES measurements were made on the mechanically polished (111) surface of a type IIa diamond. No emission from filled states in the fundamental gap was found over the photon energy range 13.3 eV?h/ω?200 eV. This result, coupled with the sharp 1×1 LEED patterns which were obtained and the relative cleanliness (of elements which can be detected by AES) of the diamond (≲1 at.% oxygen, <0.5 at.% Si) suggests hydrogen termination of the lattice. Photoelectric yield measurements demonstrate the photoelectric threshold to be at band gap energy radiation. Investigation of the photoemission electron distribution curves (EDC’s) shows that, while the electron affinity at the surface is always positive, band bending is sufficient to result in an effective negative electron affinity under certain conditions. A variable surface dipole on the atomic scale, possibly due to the adsorption–desorption of a background gas, is reported. A study of the relative cross section of the upper (p‐like) versus...

Electronic structure of III-V semiconductors and alloys using simple orbitals

Abstract: A tight-binding model using four Slater or Gaussian orbitals per atom is employed along with pseudopotentials to calculate the electronic structure of zinc-blende semiconductors. Accurate band energies for the six lowest bands of GaP, GaAs, GaSb, InP, InAs, and InSb are obtained by adjusting the exponential factors in the orbitals. It is possible to generate about equally accurate band structures by using a universal basis set for all six systems. The interatomic interactions in this universal basis are found to scale as the inverse squares of the lattice parameters. This result suggests an improved virtual-crystal approximation which always gives the correct sign for the bowing parameter of the fundamental gap in ternary alloys. A procedure that modifies the Hamiltonian matrix to yield the correct effective masses and band energies near the gap has also been implemented and applied to A1As, GaP, GaAs, and InP.