Electric Field Gradients of Light Impurities in TiO2 Calculated by the Full Potential KKR Green's Function Method

The electric field gradients (EFGs) of B, N, O and Na in TiO₂ were calculated by the full potential Korringa–Kohn–Rostoker (KKR) Greens function method in the framework of the density functional theory. The agreement with the experiments was much improved from the previous calculations that were based on the muffin-tin potential model.     

Ab initio calculations of electric field gradients detected by impurities in TiO2, Al2O3 and CaCO3

We present ab initio calculations of electric field gradients (EFGs) at impurity sites in ionic crystals TiO₂, Al₂O₃ and CaCO₃. The electronic structure was calculated self-consistently by the KKR method in the framework of the local spin density approximation of the density functional theory. The system with a single impurity was simulated by the super cell method. It was found that EFGs for the transition metal impurities (Sc, Nb, Cd and Ta) in TiO₂ were well reproduced by the calculations if the charge state of them in TiO₂ was taken into account. The present method was applied to the determination of the implantation sites of N and O nuclei in TiO₂. The calculation of EFGs at a Si impurity in Al₂O₃ and at Ca site in CaCO₃ were used to derive the quadrupole moments of ²⁷Si and ³⁹Ca from their quadrupole coupling constants. This revised version was published online in August 2006 with corrections to the Cover Date.     

Calculation of EFGs in high Tc superconductors

The electric field gradients (EFGs) at all atomic positions of YBa₂Cu₃O₇ and YBa₂Cu₃O₆ are calculated on the basis of full potential linearized augmented plane wave calculations by an ab initio method. Cood agreement with experimental EFG_s is found for all oxygen positions in YBa₂Cu₃O₇ and the Cu1 position in both compounds, while for the Cu2 position in the superconductor the symmetry of the EFG agrees with experiment but the magnitude of our theoretical EFG is only half the experimental value. A small transfer of 0.07 electrons from d(x²−y²) to d(z²) symmetry would be sufficient to achleve agreement with experiment. Thus the underlying local density approximation is not perfect, but remains a very accurate method for describing ground state properties.     

Low-spin states of odd-mass xenon isotopes

In this work, we analyse the positive parity of states of odd-mass nucleus within the framework of interacting boson-fermion model. The result of an IBFM-1 multilevel calculation with the 2d_5/2, 1g_7/2, 3s_1/2, 2d_3/2 and 1h_11/2, single particle orbits is reported for the positive parity states of the odd-mass nucleus ^125–129Xe. Also, an IBM-1 calculation is presented for the low-lying states in the even-even ^124–128Xe core nucleus. The energy levels and B(E2) transition probabilities were calculated and compared with the experimental data. It was found that the calculated positive parity low-spin state energy spectra of the odd-mass ^125–129Xe isotopes agree quite well with the experimental data.      

Time differential perturbed angular correlation studies of hafnium hydrides

The dependence of the electric field gradients (EFG) in Hafnium-Hydride systems as a function of the composition H/Hf in the cubic δ and tetragonal ε phases were investigated using the time-dependent perturbed angular correlation (TDPAC) technique, with¹⁸¹Ta as the nuclear probe. Two EFGs were found in the ε phase, indicating the existence of two major symmetries surrounding the Ta probe. The results indicate that the trend of the EFGs, in the ε phase, are due to the changes in the lattice parametersa _o,c _o as hydrogen is added to the Hf-H system. In the δ phase, only one major symmetry was found. Both phases are characterized by broad frequency distributions and large anisotropies.     

Calculation of the electron-ion interaction-potential components linear and quadratic in the ion displacements for YBa2Cu3O7

A simple method is proposed to calculate the component of electron interaction potential with the ionic subsystem of a crystal quadratic in ionic displacement. The electron-ion interaction potential is calculated for the high-frequency A _g modes in YBa₂Cu₃O₇. The important role of the Madelung potential, which results in violation of the selection rules valid in the rigid muffin-tin approximation, is pointed out. The quadratic component of the potential can greatly affect the calculated matrix elements which correspond to electronic transitions involving absorption or emission of zero wave-vector phonons. Fiz. Tverd. Tela (St. Petersburg) 39, 1323–1327 (August 1997)     

Cluster calculations of the hyperfine properties of copper compounds

Spin-polarized ab-initio cluster procedures are used to investigate the electronic structure of CuO₂-planes in the La₂CuO₄ and YBa₂Cu₃O₇ compounds. In particular, electric field gradients (EFGs) and magnetic hyperfine interaction parameters for the Cu sites were calculated with various theoretical methods. Calculations with density functional theory reproduce the experimentally determined EFGs fairly well while those at the Hartree-Fock level generally yield values which are too large by about 40%. The anisotropic magnetic hyperfine coupling can also be calculated with reasonable accuracy. This revised version was published online in August 2006 with corrections to the Cover Date.     

Calculation of electric hyperfine interaction parameters in solids

A theoretical approach for the calculation of hyperfine parameters in solids from first principles is presented. These calculations are based on the full potential linearized-augmented-plane-wave (LAPW) band structure method, which is currently one of the most accurate schemes to determine the electronic structure in ordered solids. Exchange and correlation is treated within density functional theory using the generalized gradient approximation. Once the electron density is calculated self-consistently with high accuracy, quantities like electric field gradients (EFG), isomer shifts or hyperfine fields can easily be obtained from this density without further approximations. Using this approach we have studied various systems including metals, insulators, ionic compounds or the highT _c superconductors. In general we find good agreement between theory and experiment, which proves that our method is very accurate. Having these results in mind we are confident that this method is accurate enough to determine the value of the nuclear quadrupole momentQ, provided experimental measurements of the quadrupole coupling constant are available. This procedure is demonstrated forQ of⁷⁷Se and¹⁰⁰Rh, two nuclei recently used in PAC measurements. An extensive study of EFGs at Fe sites in various Fe-compounds has been performed leading to a very reliable quadrupole moment ofQ(⁵⁷Fe)=0.16 b, a value twice as large as that deduced from recent HF calculations but back to older estimates.     

Hyperfine interactions of 19O in TiO2 and quadrupole moments of 13,19O

The electric quadrupole interaction of ¹⁹O(I^π=(5/2)⁺, T_1/2=27.0 s) in TiO₂ single crystal was studied in detail by means of the β-NQR to determine the electric quadrupole moments Q of short-lived β-emitting nuclei ¹⁹O and ¹³O(I^π=(3/2)^-, T_1/2=8.6 ms). Two implantation sites were found for the implanted O nucleus and the quadrupole coupling constants of ¹⁹O at these sites were determined. We observed FT-NMR of the enriched stable isotope ¹⁷O in TiO₂ and obtained the electric field gradient (EFG) at the oxygen substitutional site. With this knowledge, we have determined Q(¹³O)=11.0 ± 1.3 mb and Q(¹⁹O)=3.7 ± 0.4 mb. The present results are compared with the theoretical values calculated by the shell model code, OXBASH and by the Hartree–Fock calculation with the realistic potential. This revised version was published online in August 2006 with corrections to the Cover Date.     

Calculation of diatomic van der Waals systems inert gas atom-halogen type inert gas ion in the ground state

Interatomic potentials are calculated for the systems inert gas ion in the ground state-inert gas atom Ne⁺, Xe⁺-Ne, Ar, Kr, Xe, Fr. The calculation is performed by the effective pseudopotential method using the new form of the polarization interaction potential obtained by calculating the most important polarization diagrams of perturbation theory in the Thomas-Fermi approximation. The quasimolecular states of these van der Waals systems are calculated to refine the available data; some data are obtained for the first time. Translated from ZhurnalStrukturnoi Khimii, Vol. 39, No. 4, pp. 591–595, July–August, 1998     

Electronic structure and the S K absorption spectra of chromium-containing chalcogenide spinels Cd1?xCuxCr2S4

The electronic structure and x-ray absorption spectra of sulfur in normal ferromagnetic spinels of the general formula Cd_1−x Cu_xCr₂S₄ (x=0.05, 0.1, 0.15, 0.2) are calculated using the FEFF8 program. In these calculations, the self-consistent crystal potential is simulated in terms of the partially nonlocal model of exchange-correlation potential. The model is based on the Dirac-Fock approximation for core electrons and the Hedin-Lundquist approximation for valence electrons. The S K absorption edges are calculated in the approximation of full multiple scattering by a 27-atom cluster. In addition, one-, two-, and three-scattering paths within a 981-atom clusters are taken into account. The calculation demonstrates that the introduction of even insignificant amounts of copper atoms into a CdCr₂S₄ cluster leads to a shift in the main features of the S K adsorption edges toward the high-energy range. This can be associated with variations in the nearest environment of the absorbing atom and active participation of copper ions in the chemical bonding of chalcogenide spinels. __________ Translated from Fizika Tverdogo Tela, Vol. 45, No. 4, 2003, pp. 638–640. Original Russian Text Copyright ? 2003 by Leshcheva, Safontseva, Nikiforov.     

Optics of excitons in systems with sharp heteroboundaries. Approximation of a strongly localized exciton wave function

Optical reflection spectra from a Ga_0.7Al_0.3As/GaAs heteroboundary are calculated using the approximation of a strongly localized exciton wave function. The calculation is based on electron Γ₆ and hole Γ₈ kp-Hamiltonians with position-dependent parameters. Fiz. Tverd. Tela (St. Petersburg) 40, 872–874 (May 1998)     

Contribution of three-electron diagrams of two-photon exchange to the energy of 2 s , 2 p 1/2, and 2 p 3/2 states of Li-like multiply charged ions

The contribution of three-electron diagrams of two-photon exchange to the energy of 2s, 2p _1/2, and 2p _3/2 states of Li-like ions is calculated. The consistent quantum-electrodynamic calculation is performed for the nuclear charge Z varying over a wide range with the correction for the finite size of the nucleus taken into account. All the contributions to the energy of the 2p _1/2−2s transition in Li-like ions with Z≥18 calculated to date are collected. __________ Translated from Optika i Spektroskopiya, Vol. 92, No. 3, 2002, pp. 375–384. Original Russian Text Copyright ? 2002 by Sysak, Erokhin, Shabaev.     

Modeling and calculation of the capacitance of a planar capacitor containing a ferroelectric thin film

The capacitance of a two-layer planar capacitor containing a thin layer of SrTiO₃ is calculated by conformal mapping using the partial capacitanc e method. Simple formulas are obtained for approximation calculation of the capacitances of individual components of a planar structure, and their limits of applicability are determined. A relation for the capacitance of a planar capacitor is derived which takes account of the size effect in a ferroelectric film within the context of the partial capacitance method. The calculated result is compared with the experimentally measured capacitance. Zh. Tekh. Fiz. 69, 1–7 (April 1999)     

Electron-vibrational energy exchange in collisions of Ar atoms in the 3P2 metastable state with N2(X1S g+ ) molecules

Rate constants for electron-vibrational energy exchange Ar(³ P ₂) + N₂(X ¹Σ _g ⁺, ν = 0) → Ar(¹ S ₀) + N₂(C ³Π _u , ν′), where ν′ = 0, 1, 2, were calculated. Calculations were performed taking into account the presence of a resonance in electron scattering by N₂(X ¹Σ _g ⁺). As a result, the interaction of Ar(³ P ₂) with N₂(X ¹Σ _g ⁺, ν = 0) was characterized by attraction and, in the end, intersection of electron-vibrational potential surfaces correlating with Ar(³ P ₂) + N₂(X ¹Σ _g ⁺, ν = 0) and Ar(¹ S ₀) + N₂(C ³Π _u , ν′) at interparticle distances of 2.5–3.5 ?. Exchange interaction at which electron-vibrational transitions in the region of intersection of electron-vibrational transitions in the region of intersection of electron-vibrational potential surfaces accompanied by spin exchange were induced was calculated by the asymptotic method. The rate constants determined at 300–600 K were on the order of 10⁻¹¹−10⁻¹² cm³/s and weakly increased as the temperature grew. Mainly the C ³Π _u , ν′ = 0 state of the N₂ molecule was populated. The calculation results were in satisfactory agreement with the experimental data obtained at 300 K.     

Luminescence properties of Nd<Superscript>3+</Superscript>-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in organic media

Nd³⁺-doped yttrium oxide nanoparticles (Y₂O₃:Nd) with cubic phase were obtained successfully by a glycine-nitrate solution combustion method. The results of Fourier transform infrared spectra (FTIR) showed that the –OH groups residing on the nanoparticles surfaces were reduced effectively by modifying with capping agent. The modified Y₂O₃:Nd nanoparticles displayed good monodispersity and excellent luminescence in N,N-dimethylformamide (DMF) solvent. Some optical parameters were calculated by Judd–Ofelt analysis based on absorption and fluorescence spectra. A relative large stimulated emission cross section, 1.7×10⁻²⁰ cm², of the ⁴F_3/2→⁴I_11/2 transition was calculated. Theses results show that the modified Y₂O₃:Nd nanoparticles display good luminescence behavior in organic media.     

Calculation of the spectroscopic constants for the electronic states A1Σ u+ , B1Πu, C1Πu, D1Σ u+ , and E1Σ u+ of the cesium dimer

The vibrational, rotational, and centrifugal distortion constants have been calculated for the electronic states A ¹Σ _u ⁺ , B ¹Π_u, C ¹Π_u, D ¹Σ _u ⁺ , and E ¹Σ _u ⁺ of the Cs₂ molecule. The calculation was performed on the basis of the semiempirical potential energy curves constructed in this paper. The calculated spectroscopic constants are compared with the experimental data. Original Russian Text ? A.D. Smirnov, 2007, published in Optika i Spektroskopiya, 2007, Vol. 102, No. 1, pp. 23–27.     

Computer simulation of the infrared spectra of endohedral metallofullerenes Li2C60 and Na2C60

Using the Gaussian03 computer software, the infrared spectra of endohedral Li₂C₆₀ and Na₂C₆₀ are calculated by the Hartree-Fock method in the 3–21G basis set. The calculation is carried out for three cases: (i) metallofullerenes without a solvent, (ii) metallofullerenes in a toluene solution, and (iii) metallofullerenes in a tetrahydrofuran solution. The effect of a solvent on the energetic, electrical, and spectral characteristics of the metallofullerenes is studied. Original Russian Text ? E.V. Butyrskaya, S.A. Zapryagaev, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 3, pp. 613–619.     

Determination of the optical parameters of a-Si:H thin films deposited by hot wire–chemical vapour deposition technique using transmission spectrum only

Three demonstration samples of intrinsic hydrogenated amorphous silicon (a-Si:H) films were deposited using hot wire–chemical vapour deposition (HW–CVD) technique. The optical parameters and the thickness were determined from the extremes of the interference fringes of transmission spectrum in the range of 400–2500 nm using the envelope method. The calculated values of the refractive index (n) were fitted using the two-term Cauchy dispersion relation and the static refractive index values (n ₀) obtained were 2.799, 2.629 and 3.043 which were in the range of the reported values. The calculated thicknesses for all samples were cross-checked with Taly-Step profilometer and found to be almost equal. Detailed analysis was carried out to obtain the optical band gap (E _g) using Tauc’s method and the estimated values were 1.99, 2.01 and 1.75 eV. The optical band gap values were correlated with the hydrogen content (C _H) in the samples calculated from Fourier transform infrared (FTIR) analysis. An attempt was made to apply Wemple–DiDomenico single-effective oscillator model to the a-Si:H samples to calculate the optical parameters. The optical band gap obtained by Tauc’s method and the static refractive index calculated from Cauchy fitting are in good agreement with those obtained by the single-effective oscillator model. The real and the imaginary parts of dielectric constant (ε _r, ε _i), and the optical conductivity (σ) were also calculated.     

Coupled-channel analysis for 20.4 MeV energy of p-<Superscript>64</Superscript>Zn inelastic scattering

In this study, a coupled-channel (CC) analysis of the elastic and the inelastic scattering of 20.4 MeV polarized protons from a ⁶⁴Zn target leading to the deformed 2⁺, 3−, 2₂⁺2_2^+ states was performed. The CC potential parameters and the deformation parameters of the excited states corresponding to the best fit to the experimental differential cross-sections and the analysing powers data were determined. For 2₂⁺2_2^+ excited state, a mixed type was used and a good fit to the data was provided. The CC calculation results were compared to the pure distorted wave Born approximation (DWBA) calculation results which were calculated using the new parameters. All calculations were conducted using the computer code ECIS06.