bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantum mechanical ab initio calculations of the surface structure of crystalline lithium hydride
Authors: Schulz W. , Gründler W. 
Published: July 2007

AbstractThe structure of the (100) and (110) surface of crystalline lithium hydride is calculated by the FSGO pair‐potential approximation. An outward displacement of the hydride ions and an inward displacement of the lithium ions relative to the ideal surface is determined in the case of the (100) surface. Also an alternating arrangement of the particles of the first and second surface layer is noticed. An inward displacement takes place not only for the lithium ions but also for the hydride ions in the case of the (110) surface. The surface energies and the ratio of the surface energies of the (110) and (100) surface are calculated in good agreement with semi‐empirical values of alkali halide crystals.
Madelung energies of tetragonal and orthorhombic systems
Authors: Soma T. , Umenai T. 
Published: July 2007

AbstractThe Madelung energies for tetragonal and the orthorhombic systems (simple, face‐centered, and body‐centered structures) are calculated. As applications, the stability for In which forms face‐centered tetragonal lattice, and the high‐pressure phase of group IV diamond‐type crystals are investigated.
Parameter calculation from zinc blende zone boundary conditions of CuI
Authors: Haxton M. B. 
Published: July 2007

AbstractA rigid ion, second neighbor ionic model has been proposed by Banerjee and Varshni which is successful in fitting the dispersion curves of some zinc blende structures. Additional equations are offered derived from zone boundary conditions in the [100] and [111] directions, to aid in the calculation of a dispersion curve fit. These equations are applied to CuI and parameters are chosen which fit the equations and the physical situation better than those previously suggested.
Electric paramagnetic resonance and combined resonance of conductivity electrons in InSb at 24 GHz
Authors: Rusiniak L. 
Published: July 2007

AbstractMeasurements of small samples at 24 GHz with circular electromagnetic wave polarization are performed in the 60 to 100 K temperature range. The wide resonant line on the CRA side is observed. A new interpretation of this line as a combination of lines arising from three different transitions is proposed. The transitions involve both the electric paramagnetic resonance and combined resonance. The effect of amplification for combined resonance transitions during the dynamic temperature variation is also noted.
A double d‐band model of transition metals
Authors: Zieliński J. 
Published: July 2007

AbstractA double d‐band model of a transition metal is considered and dynamic susceptibilities are calculated. A correspondence is found to the modified Zener model at least in the limiting case. The temperature dependence of the effective intraatomic Coulomb interaction Ieff is however different from that of the modified Zener model. Ieff exhibits a more or less pronounced maximum when plotted versus temperature. Consequences of such a behaviour are briefly discussed.
Multiphonon absorption in molecular crystals
Authors: Broude V. L. , Umarov L. M. , Sheka E. F. 
Published: July 2007

AbstractThe classification of molecular crystal multiphonon absorption is suggested taking into account quantitative difference of the energy spectrum of internal and external phonon modes. The experimental observations are given of phonon side bands following the bands of high frequency internal modes of the naphthalene crystal. The absorption observed is considered as a two‐phonon one caused by internal and external mode interaction. The dependence of the phonon side band shapes on the different geometry of the atom displacement for different internal modes is discussed.
On fermi resonance theory
Authors: Chisler E. V. , Davydov V. Yu. , Goncharuk I. N. , Ivanova E. A. 
Published: July 2007

AbstractStudying the resonance coupling between fundamental vibration of the molecule or crystal and one of the combinational tones the number of equations for determining the resonance parameters for nondegenerate vibrations is always less than the number of unknown variables. A method is considered which allows on the basis of one of the vibrational spectra (Raman or infrared) to reveal the resonance coupling and to obtain quantitative information about its parameters in the form of two different sets of numerical data. The choice between these sets demands additional physical information. If both Raman and Infrared spectra are available, it is possible to obtain exact quantitative information about the resonance coupling. The method is based on the study of interaction between a fundamental vibration and a system of combinational tones of the form v ± ω.
Phase transitions in the bilinear organic compounds (TTF, HMTSF)‐TCNQ
Authors: Phillips J. C. 
Published: July 2007

AbstractA variety of lattice phase transitions and conductivity anomalies are observed in the archetypical bilinear organic conductors TTF‐TCNQ and HMTSF‐TCNQ. The elastic microdomain model (EMM) explains these transitions in terms of alignments of coexisting conducting and insulating domains.
Resonant scattering of exciton‐polaritons in CdS crystals
Authors: Permogorov S. , Travnikov V. 
Published: July 2007

AbstractThe secondary emission of CdS single crystals under monochromatic excitation in the region of exciton resonance is investigated at 77 K. Rather distinct emission lines, 1LO and 2LO, shifted from the excitation energy by the energy of one and two longitudinal (LO) phonons are observed. It is shown that these lines are caused by inelastic scattering of exciton polaritons by optical and acoustical phonons. Possible mechanisms of polariton scattering and the composite character of the observed emission are discussed. The energy dependence of secondary emission efficiency, connected with two‐step scattering of primary polaritons by the exciton‐like states is compared with theoretical calculations.
One‐centre exchange potentials in a crystal (TiC)
Authors: Mokhracheva L. P. , Tskhai V. A. , Geld P. V. 
Published: July 2007

AbstractA method of constructing the exchange potential in a crystal as a superposition of effective one‐centre exchange potentials is considered. Avaraging is used over atomic wave functions located on different lattice sites. The results obtained are compared with atomic exchange potentials calculated by the Slater approximation and by averaging the exchange term in the atomic Hartree‐Fock equation.
Mixing of frenkel excitons and ionic excited states of a linear molecular crystal with two molecules in the unit cell I. General model
Authors: Petelenz P. 
Published: July 2007

AbstractThe Merrifield theory of the interaction between the neutral and ionic excited states of a linear molecular crystal is generalized for crystals with two molecules in the unit cell. It is demonstrated that the Hamiltonian can be split into three communting terms. For two of them the original Merrifield theory is directly applicable and its conclusions are valid. The third term describes the mixing between the (+) Davydov component of the Frenkel exciton, the (+) intra‐cell CT exciton, and the (+) lengthwise and (+) crosswise ionic pair states. It can no more be treated within the frame of the original Merrifield theory. However it can be further transformed to a renormalized form which consists of two decoupled Hamiltonians. Both of them are formally analogous to the Merrifield Hamiltonian but with renormalized effective parameters. In the result some ionic states become active in the absorption spectrum.
Optical phonons in AgGaSe2
Authors: Miller A. , Holah G. D. , Dunnett W. D. , Iseler G. W. 
Published: July 2007

AbstractPolarised infrared reflectivity measurements are made on a single crystal of the chalcopyrite compound, AgGaSe2. This is the only selenium I—III—VI2 compound so far investigated for zone centre phonon properties. They are compared with previous studies of lattice dynamics in the sulphide family and its binary zinc blende analogues. Four modes having E irreducible representation are observed between 35 and 75 μm with the light polarised perpendicular to the c‐axis, while two B2 modes are observed in the range 35 to 65 μm with the light polarised parallel to the c‐axis. A classical dispersion harmonic oscillator computer fit is made to the data to give the oscillator parameters.
Localization theory for the random weaire model
Authors: John W. , Schreiber J. 
Published: July 2007

AbstractThe localization theory of Economou and Cohen is applied for the random two‐band Weaire model of amorphous covalent semiconductors. Several approximations for the localization function L(E) are calculated in the case of Lorentzian distribution potential parameters. The behaviour of the mobility edges in dependence on the strength of fluctuations are studied in comparison with the shape of the density of states.
A study of the band structure of graphite based on the rigorous cellular method
Authors: Wegener W. , Fritsche L. 
Published: July 2007

AbstractA band structure calculation for a single layer of graphite is presented. The computation is carried out from first principles and requires four basic informations, i.e. the lattice constant and the lattice symmetry of the layer, the stacking distance of consecutive layers, and the atomic number of carbon. Altmann's rigorous cellular method is used to obtain the band states and the energy bands. It is shown that this method can be simply modified to include non‐muffin tin parts of the potential to a large extent. Hence, the results may be compared with earlier calculations based on the discrete variational method. As to the agreement with experimental data on the band structure of graphite, both methods seem to work equally well. It is assumed however, that the cellular method has some advantages as regards the accuracy of the wave functions obtained and its wider range of applicability. The results of the present work demonstrate that this method is competitive also for open and highly anisotropic structures and is not restricted to close‐packed or nearly close‐packed lattices, as has often been suspected.
X‐ray spectroscopic investigation of the electronic structure of MgCu alloys
Authors: Neddermeyer H. 
Published: July 2007

AbstractThe Mg Kβ, Mg Kα1,2, and Cu Lα1,2 emission spectra are measured of Mg90Cu10, Mg80Cu20, Mg2Cu, MgCu2, and of the pure metals. In the MgKβ spectra of the Cu‐rich alloys on the low energy side of the main maximum a second maximum is observed, which can be related to the Cu d‐electrons. The position of the MgKα1,2 doublet shows a very small shift to higher energies with increasing Cu concentration. The Cu Lα1,2 spectra show a narrowing with decreasing Cu concentration. The shape of the valence band spectra can be qualitatively explained by recent calculations.
Relationships between the nonradiative multiphonon carrier‐capture properties of deep charged and neutral centres in semiconductors
Authors: Pässler R. 
Published: July 2007

AbstractOn the basis of a certain set of empirical trap‐structure parameters, an analytical description is given of nonradiative multiphonon capture and ejection processes (Shockley‐Read processes) occurring at deep traps in direct and indirect semiconductors. The mechanism‐specific connections between the capture properties of charged and neutral centres are represented in terms of suitably defined temperature‐averaged Sommerfeld factors. These factors are, within the approximation of an isotropic effective free‐carrier mass, calculated explicitly both for attractive and repulsive centres.
Shubnikov‐de Haas investigations on n‐type Bi2(SexTe1−x)3
Authors: Köhler H. , Haigis W. , von Middendorff A. 
Published: July 2007

AbstractShubnikov‐de Haas magnetoresistance oscillations are observed in the mixed crystal system Bi2(SexTe1−x)3 for 0 < x ≦ 0.1 and 0.8 ≦ x < 1 at temperatures between 1.7 and 4 2 K in magnetic fields up to 10.5 T flux density. The electron concentrations ranged from 5 × 1017 to 6.5 × 1019 cm−3. In both the separate ranges (Te‐rich and Se‐rich composition) the electronic mass parameters are essentially unchanged compared to pure Bi2Te3 and Bi2Se3, respectively. For the Te‐rich side the energy gap between the lowest conduction band and the postulated second type of conduction band valleys decreases with increasing selenium content. The evaluated g‐tensor ellipsoids correspond to the results for n‐Bi2Te3 in the region 0 < x ≦ 0.1.
Entropy production and choice of heat flux for degenerate semiconductors and metals
Authors: van Vliet K. M. 
Published: July 2007

AbstractThe concept of heat flux in multi‐band solids, having built‐in fields, is definable in various ways, depending on which energies are included in the transport. First the macroscopic entropy balance is examined, though more insight is gained from a microscopic picture. To this purpose the entropy flux and production function are computed for a degenerate nonuniform electron gas from the Boltzmann equation, using the streaming‐vector method, up to first order terms. From this a consistent picture of total energy, internal energy, and entropy transport emerges. The Boltzmann H‐theorem for electron—phonon interaction is also briefly discussed.
Lattice dynamics of AgBr at 295 K
Authors: Singh R. K. , Singh K. P. 
Published: July 2007

AbstractThe lattice dynamics of silver bromide at 295 K is studied with the three‐body‐force shell model which is adequately capable to account for the Cauchy violation and interatomic interactions in ionic crystals. The results calculated from this model are found to agree reasonably well with the measured data on the dispersion of phonons, two‐phonon Raman‐scattering, and infrared‐absorption spectra. The model reveals the physical properties equally well both at 80 and 295 K.
Influence of uniaxial stress and electron—electron scattering on the phenomenological conductivity relaxation time in n‐type germanium
Authors: Dienys V. , Kancleris Ž. 
Published: July 2007

AbstractThe dependence of the phenomenological conductivity relaxation time τσ on the compressive uniaxial stress F applied in 〈111〉 direction is investigated in n‐type Ge. The measurements at 80 K are made for two groups of samples with free carrier concentrations of 5 × 1012 cm−3 and 2.4 × 1014 cm−3. At intermediate stresses (0 to 5 kbar) a nonmonotonous dependence of τσ on F is observed. It is shown that this effect is mainly caused by the influence of stress on the inertia of the electric field‐induced electron redistribution process. At stresses F > 5 kbar τσ asymptotically approaches a saturation value which increases with electron concentration. The qualitative analysis of these data leads to the conclusion that the coupling constants for the electron scattering by the electrons of the same and of the other valleys are of the same order.
Raman scattering by KI containing F centres
Authors: Buisson J. P. , Lefrant S. , Sadoc A. , Taurel L. , Billardon M. 
Published: July 2007

AbstractRaman spectra of KI (F centres) are described and calculated in the “off resonance” approximation neglecting the spin of the F centre electron. The theory predicts a very intense Γ resonant mode at 96 cm−1 in agreement with the experiment but is unable to account for the observed depolarization of this mode. Application of Henry's theory shows that this effect can be partially due to the spin—orbit coupling of the F centre in its first excited state.
The electronic states in molybdenum
Authors: de Hosson J. Th. M. 
Published: July 2007

AbstractA method is given for calculating the electronic states in molybdenum. The formalism of the multiple scattering theory (SCF‐Xα‐SW) forms the basis of this method. The charge densities in each point of a cluster of nine Mo atoms are determined by superimposing atomic densities calculated by the Dirac‐Slater formalism. For the purpose of comparison similar results are obtained from the relativistic and non‐relativistic Hartree‐Fock model. From photo‐emission and optical reflectance measurements of Mo it is concluded that the energy levels are at −0.037, −0.118, −0.287 Ryd below and 0.290 Ryd above the Fermi level. The corresponding values calculated are −0.041, −0.128, −0.238 Ryd below and 0.209 Ryd above it. The results are in good agreement with those obtained using APW technique.
Non‐linear absorption of electromagnetic waves by band charge carriers in a laser field
Authors: Fomin V. M. , Pokatilov E. P. 
Published: July 2007

AbstractThe absorption of a probe electromagnetic wave by charge carriers is discussed leading to intra‐band transitions in a laser field in the presence of a magnetic field. The absorption coefficient is calculated for different scattering mechanisms at arbitrary temperatures using the path‐integral method. A stationary combination of the phases of the probe and laser waves is shown to cause an additional absorption. The dependence of the absorption coefficient on the magnetic field applied is studied. The influence of scattering mechanism, type, and reciprocal orientation of polarizations of both the waves on the absorption non‐linearity pattern is analyzed. The change of the probe wave polarization due to the anisotropy of the nonlinear absorption is found. The effects discussed can be used for an effective identification of the main scattering mechanism as well as for an investigation of the charge carrier plasma state.
Paramagnetic domain tips in quasi‐one‐dimensional conductors
Authors: Phillips J. C. 
Published: July 2007

AbstractFits to the paramagnetic susceptibility of three mixed valency planar (MVP) compounds with columnar structure and one‐dimensional metallic conduction properties reveal discontinuities in Curie constants for which no explanation is available. This discontinuity corresponds to a third‐order phase transition, which is explained here as intrinsic and as associated with the lateral alignment of paramagnetic domain tips.
On the domain structure near the penetration field of the intermediate state in type‐I superconductors
Authors: Fahnle M. , Kronmller H. 
Published: July 2007

AbstractThe radius r and the distance a of the flux tubes in the triangular flux‐tube lattice of type‐I superconductors are determined within the framework of the Ginzburg‐Landau theory as functions of the applied magnetic field, the surface energy parameter, Δ, and the thickness, L, of a superconducting layer in the limit N → 1 (N demagnetizing coefficient of the sample, 0 ≤ N≤ 1). It is shown that near the penetration field of the intermediate state the Gibbs free energy of the flux‐tube structure is lower than that of a laminar domain structure.
Energies and fermi level of electrons in thin size‐quantized metal films
Authors: Sculte F. K. 
Published: July 2007

AbstractThe energies and the Fermi levels of electrons in thin size‐quantized metal films are investigated. Frequently a model with a constant potential is used and it is demanded that the wave functions or their derivatives vanish on planes parallel to the film surfaces. The position of these planes relative to the ion lattice is determined from the condition that the Fermi energy does not include a term inversely proportional to the film thickness. A comparison with numerical results of a fully self‐consistent calculation reveals that the results for the case that the wave functions vanish on the bounding planes (Dirichlet boundary conditions) form a satisfactory approximation.
Surface polariton effects in spontaneous emission
Authors: Agarwal G. S. , Vollmer H. D. 
Published: July 2007

AbstractAnalytic expressions of a previous paper, for the width of the excited state of an atom in presence of a dielectric interface are integrated numerically for two different types of material medium viz. a metal and the one involving phonorus such as GaP. In each case there is a very large transition probability that the atom decays with the emission of an appropriate surface polariton. It is also found that the diffuse contribution to the width closely related to the irradiated power is much smaller than the surface polariton contribution. The influence of the damping of the dielectric function on the width of the atomic states as well as the surface plasmon‐polariton contribution to frequency shifts for a metal are studied.
On the theory of exciton absorption in amorphous semiconductors
Authors: Majerníková E. 
Published: July 2007

AbstractAn investigation is made of the exciton effects, including the effect of the deformation of the internal state due to “collisions” with the random barriers in the case when ϱ ∼ L ‐ De, on the absorption coefficients of amorphous solids characterized by a Gaussian random potential. The factor exp [η2(1  αnl) β2] in the density matrix due to the random potential, appearing in this case, is shown to be responsible for an approximately Gaussian shape of the absorption edge.
The charge‐ordered state and collective excitations
Authors: Ionov S. P. , Lubimov V. S. , Manakova L. A. , Mironov V. S. , Makarov E. F. 
Published: July 2007

AbstractThe spectrum of collective excitations is investigated for the charge‐ordered state of the first type, when the constants of the intra‐ and inter‐site interactions correspond to electronic repulsion. Taking the interband exchange interaction into account the lower boundary of the spectrum is calculated and the conditions are determined when the collective mode is within the energy gap. It is shown that the considered excitations cause instability of the charge‐ordered state with respect to the transition into the Mott state, and the conditions of existence of such an instability are found. The collective spectrum of a one‐dimensional crystal at T = 0 is studied.
Acceptor ground states in nearly cubic semiconductors
Authors: Schmidt Martin 
Published: July 2007

AbstractThe splitting of acceptor ground states and their energy shift under the influence of uniaxial stress or noncubic crystal fields are calculated on the basis of a spherical or cubic valence band structure with large spin‐orbit splitting. The knowledge of the band parameters and the perturbation induced valence band splitting is sufficient to estimate the energies of the ground and first excited acceptor states. The experimental determination of the deformation potentials of three shallow acceptors in GaAs as well as the quadratic dependence of the acceptor ground states on the uniaxial stress provide a direct check of the calculations.
Spherical effective impurity electron mass in Si
Authors: Sarker A. Q. 
Published: July 2007

AbstractThe spherical effective electron mass for a point charge impurity in Si is determined such that it gives the same energy as the single valley effective mass theory. A first principle screened impurity potential is used and the appropriate ellipsoidal symmetry is incorporated into the Hamiltonian by the measured transverse and longitudinal effective masses and into the pancake‐type wave function by two variational parameters.
Multiphoton absorption by charge carriers in semiconductors in a magnetic field
Authors: Fomin V. M. , Pokatilov E. P. 
Published: July 2007

AbstractA theory of absorption of strong electromagnetic radiation by charge carriers in semiconductors in a static uniform magnetic field is developed. By using the density matrix method in path‐integral representation the multiphonon absorption coefficient in semiconductors is calculated at arbitrary temperatures for different scattering mechanisms such as ionized impurities, polar and nonpolar interactions with optical phonons, and deformation and piezoelectric interactions with acoustical phonons. The coefficients of magnetic non‐linearity in weak magnetic fields are studied. The structure of the absorption spectrum in an arbitrary magnetic field is investigated, the existence of multiphoton absorption resonances revealed and the dependence of their parameters on the order of resonance and on the conditions of absorption is obtained. The asymptotic properties of the absorption coefficient in a strong magnetic field are analyzed. The anisotropy of absorption due to a magnetic field is discussed in each case.