Showing papers on "Electronic structure published in 1981"
326 citations
TL;DR: In this article, the energy band structure of black phosphorus was calculated using the tight binding approach and it was shown that black phosphorus is a narrow gap semiconductor with the direct energy gap at the zone edge in the (0 0 k z ) direction.
Abstract: The energy band structure of black phosphorus is calculated for the first time using the tight binding approach. It is shown that black phosphorus is a narrow gap semiconductor with the direct energy gap at the zone edge in the (0 0 k z ) direction. The pressure dependence of the energy gap is calculated to be -2.61 ×10 -2 eV/kbar, its experimental counterpart being -2.51 ×10 -2 eV/kbar. The optical absorption and the electrical conductivity of black phosphorus single crystals are discussed in terms of the calculated band structure.
264 citations
TL;DR: Using high resolution electron energy loss spectroscopy (EELS), the electronic excitations of benzene, pyridine, and pyrazine adsorbed on an Ag(111) surface under ultrahigh vacuum conditions were investigated in this article.
Abstract: Using high resolution electron energy loss spectroscopy (EELS), we have investigated the electronic excitations of benzene, pyridine, and pyrazine adsorbed on an Ag(111) surface under ultrahigh vacuum conditions. The molecular orientation of the adsorbed molecules is also deduced from a study of their vibrational spectra. Several electronic excitations are observed for each molecule which can be assigned as metal‐perturbed intramolecular transitions. Both singlet and triplet (π,π*) states are observed. The adsorption on the metal surface imparts minimal shifts on the transition energies of these excitations from their gas phase values. The observed energy shifts for these excitations are in dissagreement with the predictions of classical image field theory. In addition to the above ’’intramolecular’’ excitations, we find, in the case of pyridine and pyrazine, a low energy (∼2−2.5 eV), broad, onset‐like feature, which does not have a free molecule analog. Our studies show that this transition is present on...
232 citations
TL;DR: In this article, the selfconsistent electronic structures of Si, Ge, and zinc-blende GaP, GaAs, ZnS, and ZnSe have been determined using the linear combination of Gaussian orbitals method with a local-density form of the exchange-correlation functional.
Abstract: The self-consistent electronic structures of Si, Ge, and zinc-blende GaP, GaAs, ZnS, and ZnSe have been determined using the linear combination of Gaussian orbitals method with a local-density form of the exchange-correlation functional. A completely general form of the spatial dependence of the potential has been used to describe accurately the bonding character in the tetrahedral environment. Results are presented for the valence- and conduction-band energies, densities of states, effective masses, and charge densities. Comparisons are made with previous calculations and with photoemission measurements. A striking result is that the local-density theory underestimates the optical band gaps by approximately 30% or more, although the general conduction-band topology is good. The theoretical valence-band energies, charge densities, and electron and hole effective masses are also in good agreement with experiment. The energies and wave functions presented here are used to determine the optical properties of these materials in the following paper.
216 citations
TL;DR: The physical basis for valence molecular connectivity was studied and a new way of estimating valence state electronegativity is proposed from a count of exterjacent electrons divided by the quantum number squared for at least the first three quantum levels.
208 citations
TL;DR: Two states of ammonia adsorbed on Pt(111) at 100 K are distinguished by photoemission, work function, and thermal desorption measurements as discussed by the authors, where high coverage β-NH 3 hydrogen-bonds to α NH 3.
177 citations
TL;DR: The energy bands of black phosphorus, a narrow gap semiconductor with a layer structure consisting of puckered layers, were calculated for the first time using the tight binding approximation as mentioned in this paper.
Abstract: The energy bands of black phosphorus, which is a narrow gap semiconductor with a layer structure consisting of puckered layers, are calculated for the first time using the tight binding approximation. On the basis of the resulting band structure, the electronic properties of black phosphorus are discussed.
176 citations
TL;DR: In this paper, the interband optical properties of Si, Ge, GaP, GaAs, ZnS, and ZnSe were calculated using ab initio self-consistent energy bands and wave functions obtained from the previous paper.
Abstract: The interband optical properties of Si, Ge, GaP, GaAs, ZnS, and ZnSe were calculated using ab initio self-consistent energy bands and wave functions obtained from the previous paper (paper I). Qualitatively good agreement with experiment is found, but all peak positions are shifted to lower energies since the local-density approximation underestimates the optical band gaps. Agreement with experiment with regard to line shape and peak position can be improved using an empirical energy-dependent self-energy correction as appears in the Sham-Kohn local-density theory of excitation. After examining the possible effects of lifetime broadening, our results indicate that additional many-body, excitonic, and local-field corrections must be included to achieve quantitative agreement in the intensity of certain features in the optical spectra.
164 citations
Book•
01 Jan 1981
124 citations
123 citations
TL;DR: In this paper, the authors developed new experimental methods for the determination of the thermochemical properties of organometallic species based on ion beam experiments, where an examination of the translational energy dependence of endothermic reactions yields bond energies of product species.
Abstract: The strengths of bonds formed between transition metals and
various substituent groups are of fundamental importance in the areas of surface chemistry, organometallic chemistry, and catalysis. The scarcity of such thermodynamic information has led us to develop new experimental methods for the determination of the thermochemical properties of organometallic species. Most important are ion beam experiments in which an examination of the translational energy dependence of endothermic reactions yields bond energies of product species.
TL;DR: The results of the configuration calculations of six singlet electronic states and one triplet electronic state of CO are presented in this paper, along with potential energy curves, spectroscopic constants, and electron transition moments.
Abstract: The results of the configuration calculations of six singlet electronic states and one triplet electronic state of CO are presented. The potential energy curves, spectroscopic constants, and electron transition moments are calculated, along with electronic dipole moment functions for three states. The self consistent field and configuration calculations used to obtain the electronic wave functions are described. The theoretical results are found to be in good agreement with the experimental measurements, and in the case of the dipole moment function calculations, preferable to them.
TL;DR: In this article, the experimental core level shifts in terms of chemical, relaxation and Fermi level shifts, from a combination of core level Auger and photoelectron energies, are described.
TL;DR: In this paper, the dependence of the properties of small copper clusters on their size and their relationships to the physical properties of the bulk metal have been studied through ab initio SCF calculations (with the emphasis on the clusters Cu8 and Cu13).
Abstract: The dependence of the properties of small copper clusters on their size, and their relationships to the properties of the bulk metal have been studied through ab initio SCF calculations (with the emphasis on the clusters Cu8 and Cu13). The basis set used is of double‐zeta quality for the valence shells 3d and 4s. The analysis focuses on the following properties of the clusters: geometrical structure, binding energy, and distribution of energy levels. For the 13‐atom cluster, the icosahedron is found more stable than the cubo‐octahedron corresponding to the fcc structure of the bulk metal. The binding energy per atom increases almost linearly with the number of atoms of the cluster. From the orbital energy values, the sets of 3d and 4s levels are well separated for Cu8 and just begin to overlap for Cu13. This situation looks rather different from the one for the bulk metal where the s band totally overlaps the d band. The relationship between the orbital energies from the ab initio SCF calculations and the...
TL;DR: In this paper, effective pair interactions for binary f.c. transition metal alloys have been computed using a generalized perturbation method starting from the completely disordered state, and their properties, as a function of interatomic distance, band filling, disorder and concentration are discussed.
TL;DR: In this paper, the electronic structure of semiconductor superlattices is analyzed in terms of complex bulk band structures and the details of the complex bands and the matching conditions at the interfaces are found to be crucial in energy ranges of experimental interest.
Abstract: The electronic structure of semiconductor superlattices is analyzed in terms of complex bulk band structures. The details of the complex bands and the matching conditions at the interfaces are found to be crucial in energy ranges of experimental interest. The limits of applicability of the Kronig-Penney and two-band models are shown.
TL;DR: In this paper, the MRD-CI potential curves have been calculated for C2+ in its first 16 electronic states and vertical transition energies Tv have been computed for a number of higher-lying species, all of which correlate with the first dissociation limit C(3Pg)+C+(2Pu).
Abstract: Ab initio MRD–CI potential curves have been calculated for C2+ in its first 16 electronic states and vertical transition energies Tv have been computed for a number of higher‐lying species, all of which correlate with the first dissociation limit C(3Pg)+C+(2Pu). The ground state of this molecular ion is found to be X 4Σg− while the first excited state is 1 2Πu, with a calculated Te value of 0.84 eV. On the basis of this work the C2 I.P. value known experimentally is ascribed to the a 3Πu→1 2Πu process while the transition involving both ground states appears to be difficult to detect experimentlly. Thus, the measured De value for C+2 should involve fragmentation of the 1 2Πu states as well. A comparison with previous calculations which attempt to estimate the correlation energies of the various C+2 states in a semiempirical manner shows very large discrepancies, both in the transition energies themselves and in the ordering of these states. Finally the assignment for the Meinel experimental band system at...
TL;DR: In this paper, a formalism is presented for the determination of analytic energy first derivatives for the most common types of open-shell correlated wave functions, for which the electronic structure is qualitatively understood in terms of a set of molecular orbitals which are eigenfunctions of Roothaan's restricted Hartree-Fock (RHF) operator.
Abstract: A formalism is presented for the determination of analytic energy first derivatives for the most common types of open‐shell correlated wave functions. These are the cases for which the electronic structure is qualitatively understood in terms of a set of molecular orbitals which are eigenfunctions of Roothaan’s restricted Hartree–Fock (RHF) operator. Using these RHF orbitals, configuration interaction (CI) wave functions of broad generality are included in the formalism. The method has been implemented in conjunction with the loop‐driven graphical unitary group approach. Application to the vibrational frequencies of methylene suggests that the triplet state has 0.5 kcal more zero‐point vibrational energy than does the lowest singlet state.
TL;DR: In this paper, the authors have observed quantum beats in the reversible intersystem crossing of simple α-dicarbonyls and analyzed them to obtain information concerning the density of interacting states and the average intramolecular coupling energy.
Abstract: We have observed quantum beats in the reversible intersystem crossing of simple α‐dicarbonyls, and we have analyzed them to obtain information concerning the density of interacting states and the average intramolecular coupling energy. We have analyzed most of the biacetyl quantum beats using a method based on the properties of random matrices which is described elsewhere and we present the results here. We also present an analysis based on perturbation theory using the Fourier transforms of the quantum beats which is appropriate for understanding the methylglyoxal quantum beats. The density of vibrationally hot triplet states which interact with excited singlet states that are connected to the ground electronic state via optical excitation (∼22 000 cm−1) is found to increase with the amount of vibrational excitation in the accessible singlet state at roughly the same rate as the overall density of triplet vibrational stress increases. We find satisfactory agreement between the density obtained from the quantum beats and that calculated using well known analytical formulas and direct state counting. The density of interacting states increases with the rotational quantum number of the initially excited singlet rovibronic state. The average value of the magnitude of the spin–orbit interaction is 1–10 MHz independent of the amount of vibrational–rotational excitation present. Radiationless transitions in these highly excited molecules are evidently not subject to any overriding selection rules other than spatial symmetry, and conservation of total energy, total angular momentum, and nuclear spin. The biacetyl quantum beats are collisionally quenched with helium at the same rate as the overall fluorescence. The cross section for this process is roughly 300±200 A2.
TL;DR: In this paper, a matrix Hamiltonian is derived which describes the simultaneous interaction between Σ+, Σ−, Π, and Δ electronic states and represents a generalization of the well-known Hamiltonian of the Renner-Teller effect in an isolated Π electronic state.
Abstract: Vibronic coupling between different electronic states of linear molecules is investigated by an expansion of the molecular Hamiltonian in powers of the bending amplitude ρ. A matrix Hamiltonian is derived which describes the simultaneous interaction between Σ+, Σ−, Π, and Δ electronic states and represents a generalization of the well‐known Hamiltonian of the Renner–Teller effect in an isolated Π electronic state. We discuss the influence of the vibronic coupling on the adiabatic potential energy surfaces as well as on the spectral intensity distribution for the transition from a well separated initial (linear) state into the manifold of interacting states. In contrast to the Renner–Teller effect even the linear (in ρ) vibronic coupling between Σ and Π or Π and Δ electronic states can lead to nonlinearity of the lower electronic state if the coupling is sufficiently strong. To facilitate the interpretation of the spectrum it is also calculated in the adiabatic and Franck–Condon approximations and compared...
TL;DR: In this paper, a quantum chemical framework is described where the electronic properties of model subsystems inside or at the surface of globular proteins (enzymes) can be calculated, where the protein core potential and solvent surroundings are incorporated in our effective Schrodinger equation.
Abstract: A quantum chemical framework is described where the electronic properties of model subsystems inside or at the surface of globular proteins (enzymes) can be calculated. Protein and solvent surroundings are incorporated in our effective Schrodinger equation. The theory is a generalization of the SCRF of protein core effects [O. Tapia, F. Sussman, and E. Poulain, J. Theor. Biol. 71, 49 (1978)]. A test has been carried out within the CNDO–INDO approximate scheme on the proton relay system of liver alcohol dehydrogenase. The results have elicited the fundamental role played by the protein core potential and the polarization potential in stabilizing ion‐pair structures against canonical H‐bonded ones. The polarization field introduces a nonlinear dependency on the model system wave function via the field created by its charge density. This fact is instrumental for a proper description of a highly polarized subsystem coupled to a polarizable surrounding medium.
TL;DR: In this paper, the electronic structure of amorphous silicon using a tight-binding scheme with all first and second-neighbor couplings in a continuous random network was examined and the dihedral-angle disorder was found to be important at the valence-band edge.
Abstract: We have examined the electronic structure of amorphous silicon using a tight-binding scheme with all first- and second-neighbor couplings in a continuous random network. Matrix elements and deformation potentials were taken from the crystalline band structure. The effect of bond-length and bond-angle variations is relatively small and contributes to the narrow tails at the band edges. The effect of dihedral-angle disorder was examined keeping only the nearest-neighbor interactions in the Hamiltonian. The dihedral-angle disorder was found to be important at the valence-band edge and responsible for the observed features near the top of the valence band. Topological disorder was found to have important consequences in the bulk of the bands as well as at the conduction-band edge. Apart from the effects of the bond-length and bond-angle disorder, the states at the band edges are confined within regions closely approaching the crystalline structure locally, where they have the same form as in the crystal, but do not extend through the entire structure.
TL;DR: In this article, a double zeta basis set for the N4+ ion was used to prove that there is only a single (out of six) substantially bound electronic state, the 2B2u(D2h) or 2A1(C2v) state.
Abstract: The N4+ ion is an important species in the chemistry of the atmosphere. Here N4+ has been studied theoretically using the methods of ab initio molecular quantum mechanics. There is considerable complexity involved in the theoretical study of N4+ due to (a) the fact that N2+ has two low‐lying electronic states, X 2Σg+ and A 2Πu and the order of these is reversed within the Hartree–Fock approximation and (b) there are six low‐lying electronic states of N4+. Results are first presented at the self‐consistent‐field (SCF) level of theory using a double zeta (DZ) basis set N(9s 5p/4s 2p). Both Koopmans’ theorem and direct positive ion calculations in both D2h (rectangle) and C2v (regular trapezoid) symmetry suggest only a single (out of six) substantially bound electronic state, the 2B2u(D2h) or 2A1(C2v) state. Because the D2h SCF wave function necessitates a compromise description of the N2+N2+ asymptote, the predicted dissociation energy is artificially large, although in reasonable agreement with experiment....
TL;DR: In this article, Gaussian basis sets consisting of (13s, 7p, 5d) and (14s, 8p, 7d) Gaussian functions have been optimized for the transition metal atoms of the first and second series.
Abstract: Gaussian basis sets consisting of, respectively, (13s, 7p, 5d) and (14s, 8p, 7d) Gaussian functions have been optimized for the transition metal atoms of the first and second series. The optimization criteria and the applicability of these atomic sets for molecular calculations are discussed.
TL;DR: In this article, the electronic structure of impurities in Al is calculated self-consistently by applying the density functional theory in the local spin-density approximation of von Barth and Hedin (1972).
Abstract: Using the KKR-Green function method, the electronic structure of impurities in Al is calculated self-consistently by applying the density functional theory in the local spin-density approximation of von Barth and Hedin (1972). The impurity is described by a single perturbed muffin-tin potential, which is determined self-consistently. The authors give results for the local density of states, scattering phase shifts and local charges for 3d impurities and sp-impurities (Si, P, S, Cl, Ga, Ge, As). The virtual bound states of some 3d impurities show strong deviations from a Lorentzian form arising from the band structure of Al. The impurities Cr, Mn and Fe turn out to be magnetic, with local moments of 2.0, 2.5 and 1.75 Bohr magnetons. The electronic structure of the sp impurities Si, P, Ge and As is characterised by a shift to lower energies of the s density of states, leading to localised s states for P and As, and by a filling up of the p density of states.
TL;DR: In this paper, the authors used the local spin density formalism to perform selfconsistent calculations of the electronic structure of chromium in the non-magnetic and commensurate antiferromagnetic phases, as a function of the lattice parameter.
Abstract: The author has used the local spin density formalism to perform self-consistent calculations of the electronic structure of chromium in the non-magnetic and commensurate antiferromagnetic phases, as a function of the lattice parameter. A change of a few per cent in the atomic radius brings the calculated ground state properties into agreement with experiment. The magnetisation is studied as function of volume in several models, and it is shown that a Stoner picture provides an extremely accurate description of the full calculation provided the sp-d hybridisation is taken into account. It is found that the calculated sublattice magnetisation is extremely sensitive to the exchange-correlation potential used and to the quality of the calculated state density.
TL;DR: In this article, the effect of both adiabatic and nonadiabatic changes in the electronic structure of an atom or molecule adsorbing on a metal surface is discussed.
Abstract: The effect of both adiabatic and nonadiabatic changes in the electronic structure of an atom or molecule adsorbing on a metal surface is discussed. The adiabatic aspects determine reaction paths, activation barriers, and the existence of intermediates (precursors) in the process. This is illustrated by model calculations for H2 adsorbing and dissociating on Mg (0001). The electronic excitations created are of importance for the transfer of energy between the incoming adsorbate and the substrate. Theoretical treatments of the nonadiabatic effects are discussed, and it is shown that they can easily give sticking probabilities of the other one for adsorption on metals. The possibility of using the decay of the electronic excitations via photon and electron emission to study the adsorption process is demonstrated.
TL;DR: In this article, the electronic structure and electronic spectra of azaporphyrin molecules are subjected to joint experimental and theoretical study, and a new interpretation of the azaphora's near-UV spectra in the nearUV range is given.