Showing papers on "Valence (chemistry) published in 1975"
TL;DR: Using the tight-binding method, the valence band structures and densities of states for C, Si, Ge, GaAs, and ZnSe are calculated in this paper.
Abstract: Using the tight-binding method, the valence band structures and densities of states for C, Si, Ge, GaAs, and ZnSe are calculated. Very good agreement is obtained with other calculations when all nearest- and one second-nearest-neighbor interactions are included. The effects of the various interactions on the density of states are discussed.
Mit der „tight-binding”-Methode werden die Valenzbandstrukturen und Zustandsdichten fur C, Si, Ge, GaAs und ZnSe berechnet. Sehr gute Ubereinstimmung mit anderen Rechnungen wird erreicht, wenn alle Wechselwirkungen mit nachsten und nur eine Wechselwirkung mit zweitnachsten Nachbarn berucksichtigt werden. Die Einflusse verschiedener Wechselwirkungen auf die Zustandsdichte werden diskutiert.
343 citations
TL;DR: In this article, a simple model for the magnetic susceptibility of rare-earth compounds which exhibit interconfiguration fluctuations (ICF) was presented, and the temperature dependence of the magnetic susceptibilities of several ICF Yb compounds can be fitted quantitatively, assuming an energy separation between the two configurations and an intrinsic lifetime due to the $4f$-shell-conduction-electron interaction.
Abstract: We present a simple model for the magnetic susceptibility of rare-earth compounds which exhibit interconfiguration fluctuations (ICF). It is shown that the temperature dependence of the magnetic susceptibility of several ICF Yb compounds can be fitted quantitatively, assuming an energy separation ${E}_{\mathrm{ex}}$ between the two configurations and an intrinsic lifetime $\ensuremath{\tau}$ due to the $4f$-shell-conduction-electron interaction. With the parameters ${E}_{\mathrm{ex}}$ and $\ensuremath{\tau}$ obtained from such fits it is possible to predict the temperature dependence of the valence.
297 citations
TL;DR: In this paper, the phonon-dispersion curves for the hexagonal-layered compound Mo${\mathrm{S}}_{2}$ have been measured at room temperature by inelastic-neutron-scattering techniques for the [100] and [001] directions.
Abstract: Phonon-dispersion curves for the hexagonal-layered compound Mo${\mathrm{S}}_{2}$ have been measured at room temperature by inelastic-neutron-scattering techniques for the [100] and [001] directions. The results have been analyzed on the basis of a model which includes valence forces between atoms in a layer and axially symmetric forces between atoms in neighboring layers. While the model reproduces the essential over-all features of the data, the present analysis indicates the need for a more sophisticated treatment of valence forces and/or for the inclusion of the atomic polarizabilities. The temperature dependence of the specific heat and the Debye temperature have been calculated from the model.
247 citations
188 citations
TL;DR: In this paper, two donor levels, one shallow and one deep (0.35 eV), and one acceptor level at 0.15 eV are identified and the hole mobility data are best fitted with an effective mass m p ∗≅1.3m e, which can be explained by simple, two band k. p theory if the valence band has appreciable d character.
149 citations
TL;DR: In this paper, the total width and structure of the valence bands were obtained from synchrotron radiation, and it was shown that almost all available band-structure calculations fail to predict quantitatively features other than the spin-orbit splitting.
Abstract: Photoelectron energy distributions for solid Ne, Ar, Kr, and Xe have been measured for $8 \mathrm{eV}l~\ensuremath{\hbar}\ensuremath{\omega}l~30 \mathrm{eV}$ by use of synchrotron radiation. From these we obtained the total width and structure of the valence bands. Our data demonstrate that almost all available band-structure calculations fail to predict quantitatively features other than the spin-orbit splitting. Photoelectron energy distributions for Xe in Ar and Xe in Ne support this viewpoint.
139 citations
TL;DR: In this article, the new compounds La1−xMxMnO3 (0.05 ⩽ x⩽ 0.4), LaMnNO3.15, La0.8Na 0.8Rb 0.
137 citations
TL;DR: In this article, extensive ab initio configuration interaction calculations were carried out on the πelectron states of trans-1,3-butadiene, using a double-ζ contracted Gaussian basis set augmented with two diffuse 2p π functions on each carbon atom, which were based on a frozen σ core obtained from a ground-state SCF calculation.
Abstract: Extensive ab initio configuration interaction calculations were carried out on the π‐electron states of trans‐1,3‐butadiene. A double‐ζ contracted Gaussian basis set, augmented with two diffuse 2p π functions on each carbon atom, was used in the calculations, which were based on a frozen σ core obtained from a ground‐state SCF calculation. All excitations fro and to π orbitals were included in the CI treatment. Natural orbitals were obtained for many of the wavefunctions,and their spatial extenty was determined. Only five of the calculated excited states were found to have a valencelike charge distribution (computed vertical excitation energies in eV are given in parentheses): 1 3Bu (3.45), 13Ag(5.04), 21Ag(6.77), 33Bu (8.08), and 15Ag (9.61). These states all correlate with the valence N and T states of ethylene and can be readily described in terms of the ’’two‐vinyl model’’ as either N T (the first two) or TT (doubly excited, the last three). Except for the doubly excited 21Ag, all low‐lying singlet ex...
130 citations
118 citations
TL;DR: In this article, the geometry and vibrational frequencies of the water dimer were calculated using ab initio LCAO-SCF theory using a split valence basis set.
116 citations
TL;DR: In this article, the core levels and valence bands of Fe3C, Fe3Al and Fe3Si were investigated at temperatures ranging from 20 to 1000° and the migration of electrons from iron to carbon and from aluminium and silicon to iron.
01 Sep 1975
TL;DR: In this paper, it was shown that the appearance of two M binding energies is not in itself evidence for electronic ground-state asymmetry in a mixed-valence compound, and a model was proposed from which quantitative predictions were made.
Abstract: It has previously been assumed that an ESCA measurement on a mixed-valence-e.g., M(II)-M(III) - compound which yields two peaks for an inner-shell M ionization at energies close to those measured for separate M(II) and M(III) ions provides direct evidence that the complex has an unsymmetrical (trapped-valence) ground state rather than one in which the electrons are symmetrically delocalized. This assumption is incorrect. A complex which has a symmetrical ground state will have two accessible unsymmetrical photoionized states owing to electron relaxation in the strong field of the core hole. For a range of values of binding energy differences and electron coupling parameters, the photoionized states will be very nearly localized and the peak separation for a complex with delocalized ground state will be close to that for isolated M(II) and M(III) ions. The appearance of two M binding energies is thus not in itself evidence for electronic ground-state asymmetry in a mixed-valence compound. A model is proposed from which quantitative predictions are made.
TL;DR: In this paper, the valence ionization potential of pyridine and phosphoridine is studied by an ab initio many-body approach which includes the effects of electron correlation and reorganization beyond the Hartree-Fock approximation.
TL;DR: In this paper, the authors derived approximate partial densities of valence states for AgCl and AgBr for photon energies of 16.8, 21.2,,26.9, 40.8 and 1486.6$ eV.
Abstract: AgCl and AgBr have been investigated by photoemission for photon energies $h\ensuremath{
u}=16.8, 21.2, ,26.9, 40.8, \mathrm{and} 1486.6$ eV. By exploiting the strong dependence on $h\ensuremath{
u}$ of the photoionization cross sections for the atomic orbitals composing the valence bands, we have been able to deduce approximate partial $p$ and $d$ densities of valence states for these compounds. The most conspicuous feature of the photoelectron distribution curves is a sharp peak near the center of the valence band, which our partial density of states shows to be mostly $d$-like. The $p$ density of states exibits two main peaks centered at 2- and 5-eV binding energy and a gap at the energy of the sharp $d$ peak. From the $p$ and $d$ densities of states we conclude that, except for the sharp $d$-like peak and the associated $p$ gap, the $p$ and $d$ functions are nearly equally and uniformly mixed throughout the valence band. The results are compared with partial densities of states calculated with a simplified tight-binding scheme and the band structure is discussed in detail.
TL;DR: In this paper, a procedure for generating approximate valence and Rydberg orbitals from spectral data is extended to continuum states, and the predicted values are shown to be in good agreement with experimental and polarized Hartree-Fock values, and results generally superior to cross sections obtained from the same spectral data by the quantum defect method.
Abstract: A previously described procedure for generating approximate valence and Rydberg orbitals from spectral data is extended to continuum states. Formulas for photoionization cross sections are derived, and cross sections are reported for the lithium sequence ions (Li I to Si XII), sodium, and helium. The predicted values are shown to be in good agreement with experimental and polarized‐Hartree–Fock values, and results are generally superior to cross sections obtained from the same spectral data by the quantum defect method.
TL;DR: In this article, molecular orbital calculations performed using the SCF X α Scattered Wave Cluster method are presented for the octahedral oxyanions MgO 6 −10, Al O 6 −9 and SiO 6−8.
TL;DR: In this article, the authors presented a detailed study based upon a second-neighbor tight-binding calculation using the same starting point as that used earlier by Stocker and by Shevchik, Tejeda, and Cardona.
Abstract: We present a detailed study based upon a second-neighbor tight-binding calculation using the same starting point as that used earlier by Stocker and by Shevchik, Tejeda, and Cardona. Parameters are fit to the known bands of the group-IV semiconductors; symmetric matrix elements are assumed constant in isoelectronic series while the variation of antisymmetric matrix elements with polarity is obtained directly from the bond-orbital model of Harrison. Using these parameters, valence bands are obtained for all zinc-blende semiconductors. The agreement with experiment for symmetry-point eigenvalues is comparable to that of the empirical-pseudopotential method though the bands are obtained analytically. As expected, agreement for effective masses and for nonsymmetric points is not as good. From the various symmetry-point expressions for the bands several relationships between eigenvalues within a given band are obtained. By dissecting the interbond matrix elements into matrix elements between $s {p}^{3}$ hybrids, a number of relations between eigenvalues in different materials are obtained; these take the form of dependence upon polarity for isoelectronic series and dependence upon bond length for compounds of equal valence difference. Additional insight into the origin of these trends is obtained by further dissecting the interhybrid matrix elements into matrix elements between atomic orbitals. It is found that the convergence of the tight-binding calculation increases with increasing polarity but is quite insensitive to metallicity; an explanation for these tendencies is given.
TL;DR: In this paper, the platinum-like catalytic activity of WC was reconciled by using soft X-ray appearance potential spectroscopy to reconcile the different observations concerning the platinumlike electronic structure found in Xray photoelectron spectra.
15 Dec 1975
TL;DR: In this article, a theory for the mixed valence state of rare-earth compounds is presented, which includes two types of electronic states-localized, highly correlated states and itinerant, non-correlated states.
Abstract: A theory for the mixed valence state of rare-earth compounds is presented. It includes the following features: (1) two types of electronic states-localized, highly correlated states and itinerant, non-correlated states; (2) a very strong Coulomb repulsion between localized states in the same site; (3) a Coulomb interaction between localized and itinerant states which drives the phase transition; and (4) hybridization between localized and itinerant states which produces the mixed valence state. It is shown that this model produces (a) at T = 0, a variation in the number of localized electrons which may vary in a smooth or in a discontinuous fashion as a function of pressure or alloying; (b) transitions at finite temperature which terminate in a classical critical point. Qualitative agreement with experiment is an encouraging feature of the model.
TL;DR: In this paper, the potential surfaces for ground and excited states (below 11 eV) of acetylene are computed with an ab initio frozen core method. Various planar and non-planar geometrics are investigated.
TL;DR: In this article, molecular photoemission spectra of the valence orbitals of HF, CH4, CH3F, CH2F2, CHF3, and CF4 were taken using the 132.3 eV Mζ line of yttrium.
TL;DR: In this article, the reaction of Aquopentaamminruthenium(II)-hexafluorophosphat with 4,4′-Bipyridyl im Verhaltnis 2 : 1 unter Argon liefert den Komplex (Ia), der durch Oxidation mit Brom in (Ic) ubergeht, das als Tosylat gefallt wird.
Abstract: Die Reaktion von Aquopentaamminruthenium(II)-hexafluorophosphat mit 4,4′-Bipyridyl im Verhaltnis 2 : 1 unter Argon liefert den Komplex (Ia), der durch Oxidation mit Brom in (Ic) ubergeht, das als Tosylat gefallt wird.
IBM1
TL;DR: In this paper, the relationship of the unusual stoichiometry of (TTF)Br 0.71−0.76 to the degree of charge transfer in 1 : 1 Π-donor/ TCNQ salts is examined and discussed.
TL;DR: In this article, X-ray photo-emission spectroscopy (XPS) was performed on thin films of Si3N4 deposited on Si using carrier injection from low-energy corona ions and a shallow junction detector.
Abstract: Transport measurements were performed on thin films of Si3N4 deposited on Si using carrier injection from low‐energy corona ions and a shallow junction detector. Large hole conduction is found for both corona polarities. Examination of the electronic structure of Si3N4 by x‐ray photoemission spectroscopy (XPS or ESCA) reveals one broad structure 10 eV wide (FWHM) at the top of the valence bands which results from the bonding of the Si 3s, Si 3p, and N 2p orbitals. This finding is consistent with the hole conduction we observe. The XPS results are compared with those from amorphous SiO2. The tops of the valence band of Si3N4 and SiO2 are found to lie 1.5±0.2 eV and 4.5±0.2 eV, respectively, below the Fermi level of a thin overlayer of gold.
01 May 1975
TL;DR: In this article, all-valence-electron CM calculations for a large number of electronic states of O 2 at the ground state equilibrium bond length are reported for all single and double excitations with respect to a series of most important terms in the expansion of each state.
Abstract: All-valence-electron CM calculations are reported for a large number of electronic states of O 2 at the ground state equilibrium bond length. The configuration subspaces considered include all single and double excitations with respect to a series of the most important terms in the expansion of each state. The importance of the choice of such reference configurations as well as of the use of approximate natural orbitals in these calculations is discussed Mixing at Rydberg and valence states is observed in numerous cases and the significance of this phenomenon in the interpretation of the electrons spectrum of this system is considered.
TL;DR: A survey of recent calculations involving the mixing of Rydberg and valence states in the spectra of molecular systems is undertaken in this article, where it is pointed out that when such states undergo curve crossings with one another, minimal energy splittings of 1.0-2.0 eV can occur at the respective 50-50 composition points.
TL;DR: In this paper, a qualitative interpretation of XPS and XRS data for Cu, Zn, Ga phosphides, sulphides and oxides is given, and possible reasons for phosphorus s band splitting for zinc and copper phosphides are considered.