Showing papers on "Electronic structure published in 1985"

Band gaps and electronic structure of transition-metal compounds

Abstract: A new theory is presented for describing band gaps and electronic structures of transition-metal compounds. A theoretical phase diagram is presented in which both the metallic sulfides and insulating oxides and halides occur in a quite natural manner.

First observation of an extremely large‐dipole infrared transition within the conduction band of a GaAs quantum well

Abstract: A new type of optical transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction‐band electron wave function, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption for two structures with 65‐A‐thick‐ and 82‐A‐thick wells. The transitions exhibit resonant energies of 152 and 121 meV respectively, full width at half‐maximum linewidths as narrow as 10 meV at room temperature, and an oscillator strength of 12.2. The material is anticipated to have subpicosecond relaxation times and be ideal for low‐power optical digital logic.

A first-principles theory of ferromagnetic phase transitions in metals

Abstract: On the basis of a spin-polarised density functional description of the electrons, the authors develop a 'mean-field' theory of magnetic phase transitions in metals. The one-electron-like finite-temperature Schrodinger equation is solved, formally, for random orientations of local moments and the corresponding grand potential is used in a statistical mechanics of the spin configurations. This latter, in the mean-field approximation, requires the knowledge of the electronic grand potential averaged over various ensembles of such 'spin' configurations. These averages are carried out with the help of the Korringa-Kohn-Rostoker coherent-potential-approximation (KKR CPA) method for dealing with electrons in random potential fields. Then, the whole procedure is made self-consistent on the average. The theory determines the local moment mu , the Curie temperature TC, and the susceptibility chi (q,T) in addition to the electronic structure at finite temperatures without adjustable parameters. The authors illustrate the explicit calculations for iron. The local moment is found to be 1.9 mu B above TC, and the preliminary estimate of Tc is 1250K.

The surfaces of metal oxides

Abstract: The author reviews the present understanding of the electronic, geometric and chemisorption properties of metal oxide surfaces. It is restricted to experimental and theoretical studies of single-crystal oxide surfaces since only for those systems has it been possible to correlate surface properties with specific site geometry, ligand coordination, defect structure, etc. The geometric structures of the oxide surfaces that have been investigated to date are described in relation to bulk crystal structure and cation ligand coordination. The electronic structure of both perfect and defect surfaces is discussed for the various classes of metal oxides, and similarities and differences in their behaviour are correlated with surface geometry and cation electronic configuration. The chemisorption of several types of atoms and molecules on single-crystal oxide surfaces, both nearly perfect and containing point defects is reviewed and interpreted in terms of surface electronic and geometric structure. Some recent electron- and photon-stimulated desorption results on oxides are also reviewed, as the measurements of surface phonon and plasmon modes.

Electronic Structure, Total Energies, and Abundances of the Elementary Point Defects in GaAs

Abstract: The electronic structure and total energies of eight elementary isolated-${T}_{d}$-site point defects in GaAs have been calculated with use of the self-consistent Green's-function technique. We evaluate reaction energies and from these, using simple thermodynamic considerations, we predict which native defects should be abundant in As-rich or Ga-rich and in $n$-type or $p$-type material. Comparison with available experiments confirms our findings.

Photoreflectance characterization of interband transitions in GaAs/AlGaAs multiple quantum wells and modulation-doped heterojunctions

Abstract: The optical modulation technique of photoreflectance (PR) has been applied to characterize the interband transitions in GaAs/AlGaAs multiple quantum wells (MQW) and modulation‐doped heterojunctions at room temperature. The spectra of the MQW show ‘‘derivativelike’’ reflectance features due to allowed interband transitions from heavy and light hole subbands to conduction subbands, and the E0(Γ8,v→Γ6,c) transitions of the AlGaAs layers. Our data are consistent with a square well calculation using a conduction‐band offset of 60% of the band‐gap discontinuity. For modulation‐doped heterojunctions, a correlation is observed between a PR feature approximately 18 meV above the GaAs fundamental gap and the presence of a two‐dimensional electron gas.

The electronic structure of the calcium monohalides. A ligand field approach

Abstract: The electronic structure of the calcium monohalides is addressed using a ligand field model which approximates the halide as a polarizable negative charge perturbing the one electron valence structure of the Ca+ ion. A simple, zero‐free‐parameter model is shown to predict accurately electronic energies, transition moments, permanent dipole moments, and several other molecular constants that have been experimentally determined. The molecular properties and electronic wave functions are interpreted in terms of the polarization (s/p/d/f mixing) and radial expansion (nl/n+1l mixing) of the low lying, free ion, basis functions caused by the electric field of the ligand.

Photophysics and Photochemistry in the Vacuum Ultraviolet

Abstract: Photophysics of Highly-Excited States.- 1. Introduction.- 2. Quantum Defect Theory.- 3. Core Effects.- 4. Intermolecular Rydberg Correlations.- 5. Field Effects.- 6. Rydberg States in Condensed Media.- 7. Concluding Remarks.- Methods for Studying Higher Excited States in Molecules and Molecular Crystals by Means of Synchrotron Radiation.- 1. Introduction.- 2. Properties of Synchrotron Radiation Sources: A Short Overview.- 3. Some General Aspects of Synchrotron Radiation Instrumentation.- 4. Absorption and Reflection Spectroscopy.- 5. Time-Resolved and Energy-Resolved VUV Luminescence Spectroscopy.- 6. Photoemission.- 7. Perspectives.- 8. Appendix.- Nonlinear Optics and Laser Spectroscopy in the Vacuum Ultraviolet.- 1. Introduction.- 2. Vacuum Ultraviolet Lasers.- 3. Nonlinear Optical Methods for Producing Tunable VUV Radiation.- 4. Applications to Chemical Physics.- 5. Future Goals.- Multiphoton Ionization and Third-Harmonic Generation in Atoms and Molecules.- 1. Introduction.- 2. Resonantly-Enhanced Multiphoton Ionization.- 3. Multiphoton Ionization and Third-Harmonic Generation in Rare Gases.- Electron-Impact Spectroscopy of Molecules.- 1. Introduction.- 2. General Theory.- 3. Experimental.- 4. Experimental Results.- Elements of Quantum Defect Theory. I. Introduction and Formalism.- 1. Introduction to Quantum Defect Theory.- 2. Multichannel Quantum Defect Theory in Atoms.- Elements of Quantum Defect Theory. II. A Unified Theory of Rydberg and Autoionizing States.- 1. Introduction.- 2. Eigenchannel Quantum Defect Theory.- 3. Ab initio Calculations of Quantum Defect Parameters.- 4. Applications.- Elements of Quantum Defect Theory. III. Diatomic Molecules.- 1. Introduction to Molecular QDT.- 2. Comparison with Experiment.- 3. Inclusion of Molecular Dissociation.- Negative-Ion States.- 1. Introduction.- 2. Negative-Ion Properties.- 3. Unimolecular Electron Attachment.- 4. Multiply-Charged Negative Ions.- 5. Photoabsorption by Negative Ions.- 6. Recent Studies of Long-Lived He Negative Ions.- 7. Production of Negative Ions by Photon Reactions.- 8. Collision of High-Rydberg Atoms with Electron-Attaching Molecules and the Possible Influence of Dipole Bound States.- 9. Negative Ions of Molecular Clusters.- Superexcited nd Ionic State Relaxation Processes in Vacuum Ultraviolet Excited Polyatomic Molecules.- 1. Introduction.- 2. Fundamental Processes.- 3. Competing Decay Channels of Superexcited States.- 4. Methods for Studying Superexcited and Ionic States and Their Relaxation Processes.- 5. Further Remarks on Molecular Autoionization.- 6. Decay of Ion States.- Photoionization Dynamics of Small Molecules.- 1. Introduction.- 2. Shape Resonances in Molecular Photoionization.- 3. Molecular Autoionization.- 4. Concluding Remarks.- Photodissociation Dynamics of Gas-Phase Small Molecules.- 1. Introduction.- 2. ICN Photodissociation in the Near Ultraviolet.- 3. VUV Photodissociation of HCN.- 4. VUV Photodissociation of the Cyanogen Halides.- 5. Conclusions.- VUV Spectroscopy of Rare-Gas Van Der Waals Dimers.- 1. Introduction.- 2. General Background.- 3. Experimental Apparatus.- 4. Dependence of the Cluster Ion Signals on Nozzle Stagnation Pressure.- 5. Appearance Potentials of the Dimer Ions and Dissociation Energies of the Dimer-Ion Ground States.- 6. Molecular Rydberg Structure Between the Atomic Fine-Structure Thresholds: Dissociation Energies of X+2(C 2?1/2u) and XY+(B 2?1/2 and D 2?1/2+).- 7. Molecular Rydberg Structure in the Spectra of NeY Near the Ne 3s Atomic Resonance.- 8. Molecular Rydberg Structure in the Spectra of ArKr and ArXe Near the Ar 5s and 3d Atomic Resonances.- 9. Molecular Rydberg Structure in the Spectra of X2 and XY Near the High-Lying Atomic Rydberg States.- 10. Summary and Conclusions.- Excitons and Energy Transfer in Insulators.- 1. Prologue.- 2. Frenkel Excitons.- 3. Wannier Excitons.- 4. Deep Wannier Atomic Impurity States.- 5. Excitons and Impurity States in Rare-Gas Fluids.- 6. Molecular Wannier Impurity States in Rare-Gas Solids.- 7. Excited-State Dynamics in Rare-Gas Solids.- 8. Self-Trapping of Excitons in Rare-Gas Solids.- 9. Lattice Relaxation Around Impurity States.- 10. Electronic Relaxation of Impurity States.- 11. Electronic Energy Transfer in Rare-Gas Solids.- 12. Perspectives.- Regular and Irregular Motion in Classical and Quantum Systems.- 1. Introduction: Order and Chaos.- 2. Integrable Systems.- 3. Perturbation of Integrable Systems and the KAM-Theorem.- 4. Area-Preserving Mappings.- 5. Chaotic Systems.- 6. A Generic System is Neither Integrable Nor Ergodic, But Shows a Stochastic Transition.- 7. The Birkhoff-Gustavson Normal Form and Invariant Tori Below the Critical Energy.- 8. Do Quantum Systems Exhibit Chaotic Behavior?.- 9. Integrable Systems and Tori Quantization.- 10. Quantization of Chaotic Systems.- 11. Statistics of Energy Levels.- 12. Quantizing a Generic System.- 13. Conclusions and Discussion.- New Trends in Atomic Diamagnetism.- 1. Introduction.- 2. The Coulomb Spectrum.- 3. The Landau Spectrum.- 4. The Atom in a Magnetic Field.- 5. Classical Mechanics of Diamagnetism.- 6. Quantum Mechanical Approach.- 7. Semi-Classical Methods.- 8. Experimental Studies in Atomic Physics.- 9. Prospects and Conclusions.- Evidence for Motional Electric Field Effects in the Absorption Spectrum of Lithium Vapor in a Magnetic Field.- 1. Introduction.- 2. Results and Discussion.- On the Spectrum Of V(?) $$V\left( \rho \right) = - \frac{{qt}}{\rho } + \frac{{rt}}{{{\rho ^2}}} + stp + t{p^2}.$$. Physical Implications for a Variety of Problems.- 1. Introduction.- 2. Solution of the Eigenvalue Problem.- 3. Applications.- 4. Summary.- Perturbation Spectroscopy.- 1. Introduction.- 2. Perturbation Theory and MCD Spectroscopy.- 3. Electric Field-Effect Spectroscopy.- 4. Pressure-Effect Spectroscopy.- Circular Dichroism and Magnetic Circular Dichroism Studies in the Vacuum Ultraviolet.- 1. Introduction.- 2. Instrumentation.- 3. Results.- Electric Field Studies in the Vacuum Ultraviolet.- 1. Introduction.- 2. Experimental.- 3. General Results.- 4. Excited-State Parameters.- 5. Arc-Suppressor "Solvent" Effects.- 6. Conclusions.- Valence-Shell and Rydberg Transitions in Large Molecules.- 1. Introduction.- 2. The Rydberg Concept.- 3. From Spectra to Photochemistry.- 4. Rydberg States of Transition Metal Complexes.- Multiphoton Spectroscopy and Photochemistry.- 1. Introduction.- 2. Nonlinear Photochemistry.- 3. Two Examples.- 4. Other Systems.- Excess Energy Dependence of Vibrational Relaxation and Photophysical Branching Ratios in Isolated Aromatic Molecules: Relevance to Vacuum Ultraviolet Photochemistry.- 1. Introduction.- 2. Spectral Characteristics of Gas-Phase Fluorescence.- 3. Excess-Energy Dependence of Radiationless Transitions: Theory.- 4. Excess-Energy Dependence of Radiationless Transitions: Experiment.- 5. Intramolecular Vibrational Relaxation.- 6. Photochemical Implications of the Energy Dependence of Electronic Relaxation Processes.- Theoretical Studies of the Electronic Structure and Spectra of NH3+.- 1. Introduction.- 2. Franck-Condon Analysis of the 2A1(NH3+) ? 1A1 (NH3) Spectrum.- 3. Ab initio Calculations on Low-Lying States of NH3+.- Theoretical Correlations of Organic Photochemical Reactions in the VUV.- 1. Introduction.- 2. 1,4-Cyclohexadiene.- 3. Methylene Cyclopropane.- Photochemistry of Saturated Alcohols and Open-Chain Ethers at 185 nm in the Liquid Phase.- 1. Introduction.- 2. Discussion.- Photolysis of Cyclic Ethers and Acetals at 185 nm in the Liquid Phase.- 1. Discussion.- List of Participants.

Binuclear and polymeric gold(I) complexes

Abstract: Calculs par la methode de Huckel generalisee sur [Au 2 (S 2 PH 2 ) 2 ] 2 et [Au 2 (S 2 PH 2 ) 2 ] n : structure electronique, conformation

2p absorption-spectra of the 3d elements

Abstract: The near-edge structure of the 2p absorption edges of the complete series of the 3d transition metals has been investigated by high-resolution electron-energy-loss spectroscopy. Structures in the spectra were observed that could not be resolved in previous studies. The data are compared with single-particle calculations of the 2p\ensuremath{\rightarrow}3d transition probability as well as with bremsstrahlung isochromat spectra. The comparison shows that the absorption spectra cannot be described by the density of unoccupied d states even when single-particle matrix-element effects are taken into account. Especially at the beginning of the 3d series, the interaction with the core hole is an important parameter.

Model potential calculations for second‐row transition metal molecules within the local‐spin‐density method

Abstract: The model potential (MP) method originally proposed by Huzinaga and Bonifacic is extended to spin‐polarized local‐spin‐density calculations, including scalar relativistic effects. The theoretical justification of the MP method in this case is studied and the method of optimization of the basis functions and MP parameters is given. The validity of the frozen core approximation is studied for Mo2, Ru2, and Ag2. It is found that the MP can very accurately reproduce all‐electron (AE) results if the 4p electrons of Ag and the 3d electrons of Mo are also considered as valence electrons, although inclusion of these electrons in the core still yields a useful level of accuracy. It is shown that the present MP results are not sensitive to basis set superposition errors (BSSE). Upon inclusion of the scalar relativistic effects the calculated bond length and vibrational frequency of Ag2 are in near perfect agreement with experiment, while the dissociation energy is overestimated by 23% with the ‘‘best’’ local potent...

An augmented coupled cluster method and its application to the first‐row homonuclear diatomics

Abstract: An augmented coupled cluster scheme to evaluate the higher order electron correlation effects is proposed. The method is carried out in two steps. First, a coupled cluster calculation with all double substitutions (CCD) is performed. The converged CCD wave function is then used in the evaluation of the contribution of single and triple substitutions. The method is correct to fourth order in a perturbation expansion and includes significant fifth and higher order terms. Illustrative calculations on the excitation and dissociation energies of first‐row homonuclear diatomic molecules are reported. The low‐lying excitation energies of B2 and C2 are accurately calculated. The dissociation energies of B2, C2, N2, O2, and F2 are all uniformly underestimated by 0.1–0.3 eV using large spdf basis sets.

Physical properties of amorphous materials

Abstract: One: General Properties.- Chemistry and Physics of Covalent Amorphous Semiconductors.- Fundamentals of Amorphous Materials.- Two: Structure.- The Constraint of Discord.- Structural Studies of Amorphous Materials.- EXAFS of Disordered Systems.- Moessbauer Spectroscopy - A Rewarding Probe of Morphological Structure of Semiconducting Glasses.- Dislocation Mediated Pseudo-Melting at Silicon-Metal Interfaces.- Three: Phonons.- Vibrational Properties of Amorphous Solids.- Four: Electronic Structure.- Density of States in Noncrystalline Solids.- Problems Relating to the Electronic Structure of Amorphous Semiconductors.- Five: Nonequilibrium Effects.- Nonequilibrium Transport Processes in Amorphous and Other Low Conductivity Materials.- The Peculiar Motion of Electrons in Amorphous Semiconductors.- Geminate Recombination and Injection Currents: Diagnostics for Extended State Mobility.- Light-Induced Effects in Hydrogenated Amorphous Silicon Alloys.

Hybrid electronic properties between the molecular and solid state limits: Lead sulfide and silver halide crystallites

Abstract: Tiny single PbS crystals of ∼25 A diameter are synthesized and studied optically in low‐temperature colloidal solutions. Electron microscopic examination shows a simple cubic rock salt structure with a lattice constant unchanged, within experimental error, from the bulk value. These crystallites lack the near infrared electronic absorption characteristic of bulk PbS. The small crystallite absorbance in the visible rises more steeply than does the bulk absorbance. These results reflect electron and hole localization if one considers the variation in effective mass across the band structure. A simple discussion of localization anywhere in the Brillouin zone is given. For the first time, crystallite syntheses are carried out in solvent mixtures that form transparent glasses upon cooling. The PbS spectra are independent of temperature (at current experimental resolution) down to 130 K, in contrast to earlier results for quantum size exciton peaks in ∼20 A ZnS crystallites. Previously published observations of size dependence in the excited state electronic properties of AgI and AgBr are explained as consequences of electron and hole localization in the small crystallites. AgBr appears to be the first indirect gap semiconductor to be examined in the regime where bulk properties are not fully formed.

Electron localization in alkali-halide clusters.

Abstract: The quantum path-integral molecular-dynamics method was applied to explore the structure, energetics, and dynamics of an excess electron interacting with an alkali-halide cluster. Four distinct modes of electron localization were established, which depend on the cluster composition, size, and structure; they involve an internal F-defect, an external surface state, dissociative detachment of an alkali atom, and structural isometrization induced by electron attachment.

Cohesion and structure in stage-1 graphite intercalation compounds

Abstract: We have developed a Thomas-Fermi theory for the structural and elastic properties of the first-stage alkali-metal graphite intercalation compounds We use a simplified model for the electronic structure of these materials which assumes full charge transfer between the alkali metal and the graphite, no hybridization between metal and carbon states, and a uniform distribution of the donated charge on the graphite planes We have computed lattice constants, compressibilities, shear moduli, alkali-metal diffusion constants and activation energies, and domain-wall thicknesses; general agreement with available experiments is found These results indicate that our model of the electronic properties is consistent with known elastic and structural properties The interplane metal-carbon interaction is mostly determined by a competition between Coulomb attraction and hard-core repulsion The Li ion is much more compact than that of K, Rb, or Cs, which explains the higher compressibility of the Li graphite intercalation compound and the lower Li ionic mobility The Na--C bond is found to be very soft, explaining the lack of formation of Na-intercalated graphite The in-plane alkali-metal--alkali-metal interaction is determined almost entirely by the Coulomb interaction, and is thus relatively independent of the alkali-metal species

Theoretical study of small silicon clusters: Cyclic ground state structure of Si3

Abstract: The ground state structure of Si3 is found to be cyclic (1A1, C2v symmetry) with an apex bond angle of ≂80°. The linear form, analogous to the known structure of C3, is found to be a saddle point which transforms without activation to the cyclic structure. There is a low‐lying triplet state (3A’2, D3h symmetry) which lies only a few kcal/mol higher in energy. The nature of the bending potential surface of the ground state structure is also discussed.

Electronic structure and properties of transition-metal glasses: NixZr1−x

Abstract: The linear muffin-tin orbitals (LMTO) method is used to perform self-consistent electronic structure calculations of NixZr1−x glasses for x = 36 and 59. A glass is simulated by a 39-atom cluster with periodic boundary conditions. The atoms are randomly packed and then relaxed with Lennard-Jones potentials. The calculated radial distribution functions are compared with the available experimental data. The computed electronic structure is compared with photoemission data and experimental results for the density of states at the Fermi level. The calculated results are in good overall agreement with experimental data.

Electronic structure of an isolated GaAs-GaAlAs quantum well in a strong electric field.

Abstract: An exact numerical calculation for an isolated quantum well of a GaAs-GaAlAs system subjected to an external electric field is presented. Resonance positions and widths, and density-of-states profiles are reported for a 30-\AA{} well to demonstrate that the rigorous description of the high-field states as resonances leads to qualitatively new phenomena. In particular, in fields of 4\ifmmode\times\else\texttimes\fi{}${10}^{5}$ V ${\mathrm{cm}}^{\ensuremath{-}1}$ the effective hole energy shift is reduced to zero and a new antiresonance state emerges from the continuum into the well.

Physics of small metal clusters: Topology, magnetism, and electronic structure.

Abstract: The electronic structure of small clusters of lithium atoms has been calculated using the self-consistent-field, molecular-orbital method. The exchange interaction is treated at the unrestricted Hartree-Fock level whereas the correlation is treated perturbatively up to second order by including pair excitations. This is done in two steps, one involving only the valence electrons and the other including all the electrons. A configuration-interaction calculation has also been done with all possible pair excitations. The equilibrium geometries of both the neutral and ionized clusters have been obtained by starting from random configurations and using the Hellmann-Feynman forces to follow the path of steepest descent to a minimum of the energy surface. The clusters of Li atoms each containing one to five atoms are found to be planar. The equilibrium geometry of a cluster is found to be intimately related to its electronic structure. The preferred spin configuration of a cluster has been found by minimizing the total energy of the cluster with respect to various spin assignments. The planar clusters are found to be less magnetic than expected by Hund's-rule coupling. For three-dimensional clusters, however, the magnetism is governed by Hund's rule. The effect of correlation has been found to have decisive influence on the equilibrium topology and magnetism of the clusters. The binding energy per atom, the energy of dissociation, and the ionization potential of the clusters are compared with experiment and with previous calculations. The physical origin of the magic numbers and the effect of the basis functions on the calculated properties have also been investigated.

Electronic structure of FeO and RuO

Abstract: The electronic structure of FeO and RuO is examined using multiconfiguration self‐consistent‐field (MC‐SCF) wave functions that go asymptotically to minimally correlated fragment atoms. Core electrons are eliminated by the use of relativistic effective potentials (REP) which also are used to calculate the spin‐orbit coupling constant for the 5Δ, 5Π, and 5Φ states. The electronic structure of the FeO and RuO 5Δ states is described in terms of interacting singly charged ions, M+ and O−, which are bound primarily by a strong sigma bond. The natural orbitals are determined and evaluated in detail. The characteristics of these orbitals are used to hypothesize an aufbau for the ground states of most of the first and second row transition metal oxides. In addition to the 5Δ states, the 5Σ+, 5Π, 5Φ, 5Σ−, 5Γ, 7Σ+, 7Π, 7Φ, 3Δ, 3Σ+, 3Π, and 3Φ states were also studied. FeH and RuH 6Δ, 4Δ, and 4Φ states were also examined to evaluate the basis set.

Second order perturbation correction to CI energies by use of diagrammatic techniques: An improvement to the CIPSI algorithm

Abstract: A usual procedure to get a large fraction of the correlation energy consists in the evaluation of the second order perturbation contribution to the electronic energy by utilizing as zeroth order state a moderate size CI wave function (CIPSI algorithm). A scheme of calculation based on a hole‐particle formulation of the Hamiltonian, leading to a diagrammatic pattern quite similar to the one used for the one‐determinant case, is proposed and discussed.

Multiple d‐type basis functions for molecules containing second row atoms

Abstract: The importance of multiple sets of d functions on the energy of SO2 and other molecules of Si, P, S, and Cl has been tested by comparing total energies from the SWPS set (supplementation by five sets of d functions as recommended by Stromberg, Wahlgren, Pettersson, and Siegbahn) with those obtained with one or two sets of d functions. The energy improvement due to supplementation is very sensitive to the nature of the attached atoms and to valence shell expansion but the optimum d function exponents are not appreciably affected by either of these factors. When used in conjunction with Dunning–Hay basis sets for second row atoms, supplementation by a single set of d functions provides about 80% of the self‐consistent field (SCF) energy lowering obtained with five sets; use of a second set generates about 15% more. These results are compared with the results of adding f or replacing nuclear‐centered functions with bond functions. Varying d function exponents about the optimum values produces an energy surfa...

Electronic structure of filled tetrahedral semiconductors

Abstract: We discuss the susceptibility of zinc-blende semiconductors to band-structure modification by insertion of small atoms at their tetrahedral interstitial states. GaP is found to become a direct-gap semiconductor with two He atoms present at its interstitial sites; Si does not. Analysis of the factors controlling these filling-induced electronic modifications allows us to predict that LiZnP [viewed as a zinc-blende-like (ZnP)– lattice partially filled with He-like Li+ interstitials], as well as other members of the Nowotny-Juza compounds AIBIICV, are likely to be a novel group of direct-gap semiconductors.