Line parameters and shapes of high clusters: R branch of the ν3 band of CH4 in He mixtures

The IR absorption spectra of CH₄ in pure gas and in mixture with helium were studied in the region of ν₃ band at higher J line clusters R(17)-R(22). The frequencies and intensities of rotation-vibration lines were estimated from the experimental spectra at Doppler shape conditions. The line frequencies and intensities were calculated and used for the attribution of overlapped lines in clusters. The calculated line intensities are close to the experimental values. The calculated frequency structure of the higher J manifolds are somewhat wider than the observed one. The shapes of helium-broadened line clusters were compared with those calculated accounting for line mixing. The relaxation matrix W, which is necessary in shape calculations, was constructed using semiclassical collision rate constants. The calculated shapes are in satisfactory accordance with the measured ones.     

Energy levels of single nonabrupt GaAs/AlxGa1-xAs quantum wells

Energy levels of electrons in nonabrupt GaAs/Al_xGa_1-xAs single quantum wells are calculated with and beyond the constant interfacial effective mass approximation (CIEMA), and compared with those of abrupt GaAs/Al_xGa_1-xAs quantum wells. For a given interface width, the energy levels calculated with the CIEMA are higher than those calculated beyond it, but both are higher than those of the abrupt semiconductor quantum well. The shifts of the energy levels increase with the interfacial width of the nonabrupt quantum well, as well as with the degree of interfacial asymmetry.     

Description of radiative strength functions in deformed nuclei

Radiative strength functions ofE1- andM1-transitions from ground states of doubly even deformed nuclei to states near the neutron binding energyB _n are calculated within the quasiparticle-phonon nuclear model. The wave functions of excited states include one- and two-phonon components. The calculations were made with the Pauli principle being or not included in the two-phonon components of the wave functions. It is shown that the radiativeE1- andM1-strength functions as well as the widths of giant dipole resonances in deformed nuclei are slightly influenced by the two-phonon components of the wave functions and they can be calculated in the RPA. Thek _E1- andk _M1-values are calculated for some deformed nuclei of the rare-earth and actinide region. The calculated values ofk _E1 are 1.5–2 times larger and the values ofk _M1 are somewhat less than the average values obtained in [14] from the analysis of available experimental data.     

Determination of frequencies of electron-electron collisions in aluminum heated by a femtosecond laser pulse

Heating of electrons and lattice of aluminum caused by interaction with a femtosecond laser pulse is described quantitatively. Coefficients of absorption of s- and p-polarized pulses are calculated. Frequencies of electron-electron collisions in aluminum are determined from comparison of experimentally measured and calculated coefficients of absorption.     

Theory of the angular distribution of 2pσ molecular orbital X-rays

The cross section and anisotropy of 2pσ molecular-orbital X-ray emission is calculated for 35- to 75-MeV Nb + Nb collisions. The calculated intensities are a factor of 1.5 lower than the measured ones. The 2pσ molecular-orbital X-ray anisotropy is in good agreement with experiment. When one includes the Coriolis coupling between the 2pσ and 2pπ and between the 3dσ, 3dπ, and 3dδ molecular orbitals, the 2pσ-line-tail intensity is greatly reduced below that calculated by Jäger et al., neglecting the Coriolis coupling. The implications of these calculations to the possible spectroscopy of superheavy quasi-molecules are discussed, and some suggestions are made to improve the accuracy of the spectroscopy measurements.     

Zeeman structure of the 1s5g and 1s6g configurations of helium

The splitting of levels of the 1s5g and 1s6g configurations of the helium atom in an external magnetic field (0–160 Oe) is obtained by using the fine-structure parameters calculated semiempirically. For each configuration, more than 50 crossings and three anticrossings of Zeeman sublevels are determined. The calculated splittings are compared with those obtained earlier for the 1snp and 1snd configurations of a neutral helium atom.     

Study of energy-band structures,some thermomechanical properties and chemical bonding for a number of refractory metal carbides by the LMTO-ASA method

The energy-band structures of V, Nb, VC, NbC and WC have been calculated with the use of the linearized method of “muffin-tin” orbitals (LMTO-ASA). The calculated band structures are in good agreement with a previous self-consistent APW calculation. The prominent features of the band structures for WC are a particularly wide 5d W, 2p C band, and also the presence of a separate 5d W band below the Fermi level. The values of the lattice constants, bulk moduli, sound velocities, Debye temperatures and melting temperatures have been calculated and are in reasonable agreement with experiment. It is shown that the high values of the bulk moduli of VC and NbC are explained by the hybridization between s- and p-metal states and 2s C, 2p C states, while the extreme value of the modulus for WC is due mainly to the covalency resulting from 5d W, 2s C and 2p C hybridization.     

Analysis of the polarization dependence of the N K edge X-ray absorption fine structure in InN

The polarization dependence of the x-ray absorption near-edge structure (XANES) of InN beyond the N K edge is calculated. The XANES calculations are performed for different values of the angle θ between the XY plane of crystalline indium nitride and the incident x-radiation (θ = 15°, 30°, 45°, 60°, 75°, and 90°). It is shown that, in the case of N K XANES for InN, a strong polarization dependence of the specific features of the spectrum is observed. The calculated spectra are compared with previously measured experimental spectra. The partial densities of the electronic states of InN are calculated near the top of the valence band and near the bottom of the conduction band.     

Characteristics of F centers in the ground and excited states in alkali halide crystals

The molecular-statics method and the Gourary-Adrian approach are used to calculate the displacements of the lattice ions nearest to the F center in alkali halide crystals with NaCl and CsCl structures (altogether, twenty crystals). The calculations are performed for the 1s and 2p states of the F-center electron with allowance for the angular dependence of the Coulomb potential created by the electron in the 2p state. The absorption and emission energies of the F center are calculated. The calculated energies agree qualitatively with experiment and reproduce the experimentally found tendencies of changes in these energies when going from one crystal to another.     

Ab initio calculation of the static structural properties of Be

An ab initio calculation of the static structural properties of Be is presented. The total structural energy is calculated using pseudopotentials and the local density-functional formalism with the atomic number as the only input. The lattice constant, Poisson's ratio, and the bulk modulus are predicted by calculating the total energy of the system. The deviations of the calculated results for lattice constants c, a, and c/a are approximately 1% when compared with experimental results. Poisson's ratio and the bulk modulus are also in reasonably good agreement with the measured values.     

Solid-state shifts in the L3M4,5M4,5 Auger spectra of the elements Cu TO Se

The kinetic-energy shifts between atomic and solid-state L₃M_4,5M_4,5 Auger electron spectra of Cu, Zn, Ga, Ge, As, and Se are determined with the aid of semiempirically calculated atomic and experimental solid-state Auger energies. The shift values are calculated by applying the thermochemical model to the Auger process. Good agreement is found between the calculated and experimental values.     

Systematic theoretical study of dielectronic recombination for helium-like isoelectronic sequence

Dielectronic recombination cross sections and rate coefficients of He-like isoelectronic sequence are systematically calculated employing the relativistic Flexible Atomic Code (FAC). The calculated DR resonance strengths, cross sections and rate coefficients are in good agreement with other experimental and theoretical results. The effects of radiative cascades on DR cross sections and the variation of DR branching ratio with different DR resonance and atomic numbers Z are studied. The n⁻³ scaling law is also checked and used to extrapolate rate coefficients. And analytic formulas are used to fit the total rate coefficients with respect to both T and Z for helium-like isoelectronic sequence.     

Electronic structure and the local electroneutrality level of SiC polytypes from quasiparticle calculations within the GW approximation

The most important interband transitions and the local charge neutrality level (CNL) in silicon carbide polytypes 3C-SiC and nH-SiC (n = 2?C8) are calculated using the GW approximation for the self energy of quasiparticles. The calculated values of band gap E _g for various polytypes fall in the range 2.38 eV (3C-SiC)-3.33 eV (2H-SiC) and are very close to the experimental data (2.42?C3.33 eV). The quasiparticle corrections to E _g determined by DFT-LDA calculations (about 1.1 eV) are almost independent of the crystal structure of a polytype. The positions of CNL in various polytypes are found to be almost the same, and the change in CNL correlates weakly with the change in E _g, which increases with the hexagonality of SiC. The calculated value of CNL varies from 1.74 eV in polytype 3C-SiC to 1.81 eV in 4H-SiC.     

Unified calculations of the optical and electron paramagnetic resonance spectral data for Ce ion in Y3Ga5O12 crystal

Seven crystal field energy levels (obtained from the optical spectra) and three g factors g_x, g_y and g_z (obtained from electron paramagnetic resonance (EPR) spectra) for Ce³⁺ ion in Y₃Ga₅O₁₂ crystal are calculated together by diagonalizing a complete energy matrix. The Hamiltonian of this energy matrix includes all the interactions for 4f¹ ion Ce³⁺ in rhombic crystal field and under an external magnetic field, and so the optical and EPR data can be studied in a unified way. The calculated crystal field energy levels are in better agreement with the experimental values than the calculated values in the previous paper, and the g factors (which have not been calculated previously) are explained reasonably. The results are discussed.     

On the volume dependence of the total energy and the equation of state for copper

The total energy of metallic copper as a function of the atomic radius is calculated. The model assumes that in copper one has nearly free s-electrons in OPW states and d-electrons localized at the ions in atomic-like orbitals. The coulomb interactions in the energy are calculated by using the model of neutral spheres, while the kinetic and exchange contributions to the S²-energy are approximated by the exchange charge model. Instead of the familiar Born-Mayer repulsion, which was found to lead to controversies in the case of copper, the d-type interaction energy shows a more complex behaviour having a minimum near the equilibrium atomic radius. The prediction for the cohesive energy and the equation of state is reasonable, the calculated value for the Ashcroft radius for s-electrons agrees remarkably with the ab initio estimate. The atomic-like orbitals minimizing the total energy are somewhat more extended than the real atomic wave-functions.     

The polarised frozen-core approximation: Oscillator strengths for the boron isoelectronic sequence

Orbital wave functions of a large number of ns-, np-, and nd-levels of the first five members of the boron isoelectronic sequence have been calculated using a frozen-core Hartree-Fock procedure augmented by an l-dependent core polarisation potential. The calculated ionisation energies are generally in very good agreement with observations. Electric dipole oscillator strenghts have been derived from the calculated orbitals and energies and have been used to yield simple interpolation formulae for f-values of higher members of the sequence. They are expected to be of high accuracy in many cases.     

Effect of Si substitution on electronic structure and magnetic properties of Heusler compounds Co2TiAl1−xSix

The electronic structures of Co-based Heusler compounds CoTiAl_1−xSi_x (x=0, 0.25, 0.5, 0.75 and 1) are calculated by first-principles using the full potential linearized augmented plane wave (FP-LAPW) method within GGA and LSDA+U scheme. Particular emphasis was put on the role of the main group elements. In recent years, the GGA calculations of Co₂TiAl (x=0) and Co₂TiSi (x=1) indicated that they are half-metallic, but the electronic structure of this compound with x=0.25, 0.5 and 0.75 has not been reported yet, neither theoretically nor experimentally. The calculated results reveal that these are half-metallic and exhibit an energy gap in the minority spin state and also show 100% spin polarization. The substitution of Al by Si leads to an increase in the number of valence electrons, with increasing x. Our calculated results clearly show that with the Si doping, the lattice parameter linearly decreases; bulk modulus increases, and the total magnetic moment increases. The calculated energy gap in the minority spin state, using GGA scheme, was smaller than that obtained by using LSDA+U scheme. The outcomes of this research also show that the Co-3d DOS and therefore, the magnetic properties of compounds are dependent on electron concentration of the main group elements and it will affect the degree of p-d orbital occupation.     

Theoretical investigation of zero field splitting parameters for Mn centers in ammonium tartrate

Zero-field splitting (ZFS) parameters D and E for Mn²⁺ centers in ammonium tartrate single crystal are calculated with perturbation formulae using the superposition model. The theoretically calculated ZFS parameters for Mn²⁺ at site I and site II of ammonium ion are compared with the experimental values obtained by electron paramagnetic resonance (EPR) at room temperature. The superposition model gives the ZFS parameters similar to those from experiment. The energy band positions of optical absorption spectrum of Mn²⁺in ammonium tartrate are calculated using the CFA package and crystal field parameters from superposition model. These are in good agreement with experimental energy band positions.