Useful applications of the electron localization function in high-pressure crystal chemistry

The main features of a new computational code aimed at the topological analysis of the electron localization function (ELF) in crystals are hereby presented. Besides the complete localization of all critical points, the code is able to determine the limiting surfaces that define the chemical regions associated with the so-found maxima (or attractors) of the ELF. Hence, integrations of density operators within these basins provide charges and volumes to cores, bonds and lone pairs. Two illustrative applications have been selected. Firstly, we examine the Z dependence of basin compressibilities in the elements of the first two rows of the periodic table, and secondly, we focus our attention on the chemical changes across the pathway of the zinc blende-rocksalt phase transition in BeO.     

Luminescent and dosimetric properties of ultrafine magnesium oxide ceramics after high dose irradiation

The luminescent and dosimetric properties of ultrafine MgO ≿eramics synthesized in strongly reducing conditions at Т = 1100–1400 °С are investigated. The growth of photo- and cathodoluminescence output at 2.0–3.5 eV (400–600 nm) is found. It is due to an increase in concentration of single oxygen vacancies and their aggregates. It was established that thermal treatment leads to TL intensity growth after high dose irradiation of the samples by a pulsed electron beam (130 keV). The tunneling mechanism of charge carriers' recombination occurs after this treatment as well. The presence of tunneling recombination is proved by the analysis of the shape and temperature dependence of TL isothermal decay curves. The possibility of using synthesized ceramics for high dose TL dosimetry of ionizing radiations is shown.     

Complete reorganization of the mode structure of the wave function of a channeled electron in a crystal with a superlattice

The dynamics of relativistic electrons subjected to planar channeling in distorted crystals is investigated using step-by-step numerical integration of the Schrödinger equation. It is shown that periodic distortion of a planar channel (the formation of a “superlattice”) can cause complete reorganization of the mode structure of the wave function. In the limit of weak perturbations of the crystal lattice, the simulation results are consistent with the analytical results from perturbation theory. The position of each line in the spontaneous emission spectrum in the case of resonant distortions depends on the length of the superlattice period.     

Synthesis,X-ray crystal structure and optical properties research of novel diphenyl sulfone-based bis-pyrazoline derivatives

A series of novel bis-pyrazoline derivatives were synthesized by the reaction of chalcone and (sulfonylbis(3,1-phenylene))bis(hydrazine) in 20–34% yields. The structures of the compounds were determined by IR, ¹H NMR, HRMS spectra, and a representative compound 3b was confirmed based on the X-ray crystallographic analysis. Absorption and fluorescence spectra of these compounds in dichloromethane solution were investigated. The results showed that the emission maxima varied from 415 to 444 nm mainly depending on C3 substituents of pyrazoline moiety. The compounds had higher quantum yields, when C3 substituent was an electron-withdrawing p-chlorophenyl group. Moreover, absorption spectra and emission spectra exhibited a blue-shift and a red-shift with increasing the polarity of solvents, respectively. Fluorescent molecules happened to collide with each other and resulted in quench of the fluorescence when the concentration increased over to 10^?5 M.     

Superconducting transition in polysulfur nitride as a function of crystal quality

The superconducting transition temperature in polysulfur nitride crystals of various quality appears invariant between 0.26 and 0.28°K, but the completeness of the transition varies from sample to sample. A residual resistance remains in bulk samples which reflects the density of fiber segment junctions.     

Inhomogeneous polarizable medium as a model for an electron gas in a nonconducting crystal

The response of the electron system to an external perturbation in an insulating medium is considered in the context of the electron density functional method. The energy functional minimization relies on the proper choice of the trial function considering different spatial scales of the electron polarization. An efficient scheme for the density functional parametrization is suggested. The electron response to atomic displacements and external electric fields has been calculated for a simple model of electron polarization centers embedded into the homogeneous dielectric background. Good agreement with the experiment is achieved for the phonon spectra ofSi, Ge, and α-Sn. The electron density induced in the external homogeneous electric field is in good agreement with that calculated by the well-known ab initio methods. V. D. Kuznetsov Siberian Physical-Technical Institute at Tomsk State University. Translated for Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6 pp. 30–37, June, 1999.     

Luminescent properties of erbium-activated glasses

The spectra, intensity, and duration of trivalent erbium luminescence in a large number of inorganic glasses of various compositions were investigated. The observed absorption and luminescence bands were attributed to transitions between certain^sL_j levels of the Er³⁺ ion. It is shown that in all cases the principal portion of the luminescence yield was associated with the⁴I_13/2 ⁴I_15/2 transition band with _max = 6500 cm^–1. The effects of glass composition, activator concentration, and temperature on the yield and duration of luminescence in the 6500 cm^–1 band were studied. An investigation of the effect of temperature on the structure of this band was used to construct a diagram of the crystalline splitting of the⁴I_13/2 and⁴I_15/2 levels in glass.     

Radiation from a channeled electron in a crystal

Results are presented on the yield of photons in the low-energy part of the spectrum produced by electrons of energy E₀=800 MeV in a diamond single crystal. Photon spectra and orientation curves are used to show that emission occurs during channeling in this energy range.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 117–121, November, 1978.     

The electronic structure and the ferromagnetic intermolecular interactions in the crystal of a diphenyl nitroxide derivative

Based on the generalized gradient approximation, full potential linearized augmented plane-wave calculations have been performed to study the electronic band structure and the ferromagnetic (FM) interactions of the 9,9-dipropyl-9,10-dihydroacridin-10-yloxyl (DPAO) organic radical. The total and partial density of states and the atomic spin magnetic moments are calculated and discussed. It is found that the unpaired electrons in this radical are localized in a molecular orbital constituted primarily of the π* (NO) orbital, and the main contribution of the spin magnetic moment comes from the NO free radical, with little contributions from other C atoms. The origin of FM interactions is also studied in detail.     

电子相对论径向波函数的基本特征

利用相对论平均自洽场理论,研究了电子相对论径向波函数的基本特征.电子相对论径向波函数大小分量的数量级通常相差悬殊且不"同步",核外电子的径向分布没有严格的零概率点;束缚电子相对论径向波函数大小分量的节点个数为n-l-1、波腹个数为n-l,而自由电子的节点和波腹数则趋于无穷大.电子相对论径向波函数反映了相对论效应的基本特征:相对论效应越强,小分量振幅相对越大,自由电子径向波函数振荡越剧烈.     

Variation of the peak temperature at the maximum as a function of dose in thermoluminescent phosphors

A feature of the second and general-order kinetics equations is the shift of the peak temperature at the maximum towards lower temperatures as the dose increases. In this article, this effect is theoretically discussed. Some hypotheses are also given in order to explain this behaviour.     

Inelastic electron tunneling spectroscopy: Intensity as a function of surface coverage

Inelastic election tunneling spectroscopy (IETS) is a sensitive technique for obtaining vibrational spectra of molecules adsorbed on an oxide surface and incorporated into a metal-oxide-metal tunnel junction. IETS energy data are used routinely. However, IETS intensities contain additional information which, for theoretical and experimental reasons, has not been used systematically. This paper examines the variation of IETS intensity with surface coverage of dopant molecules in the junction, a relationship of practical and theoretical importance. IET spectra are taken using standard experimental techniques and a liquid doping technique which allows the surface coverage to be determined independently. From an analysis of a large number of modes of benzoic acid on alumina, it is found that IETS intensity, defined in the usual way as the normalized change in conductance, $\text{Δ σ}\text{σ}$, is a nonlinear function of surface coverage. A physical model is presented which attributes this behavior to a difference in elastic tunneling conductances through empty or filled regions of the dopant layer in a junction with a fraction of a monolayer coverage. In addition, the liquid and vapor doping techniques in common use in IETS are discussed in terms of statistical mechanics and are shown to be manifestations of the same basic phenomenon.     

Radiation dose rates in Space Shuttle as a function of atmospheric density.

Current models of the inner trapped belt describe the radiation environment at times of solar minimum and solar maximum, respectively. These two models were constructed using data acquired prior to 1970 during a small solar cycle, and no valid model for the past two high solar cycles exists. There is a clear need to accurately predict the radiation exposure of astronauts at all times between the solar minimum and solar maximum, not only on the short duration Space Shuttle flights, but on the longer term stay onboard the Mir orbital station and the planned International Space Station (ISS). An analysis of the trapped absorbed dose rate, D, at six fixed locations in the habitable volume of the Shuttle shows a power law relationship, D=A rho-n, where rho is the atmospheric density, rho. The index, n, is weakly dependent on the shielding, decreasing as the average shielding increases. A better representation is provided by D=A tan-1 [(Xi-Xi c)/(Xi c-Xi m)], where Xi=ln(rho), and A, Xi c, and Xi m are constants. Xi c is related to the atmospheric density near the altitude of atmospheric cutoff. These relationships hold over nearly four decades of density variation and throughout the solar cycle. This then provides a method of calculating absorbed dose rate at anytime in the solar cycle. These empirically derived relations were used to predict the dose rates for eleven Space Shuttle flights carried out since January 1997. The predictions are in excellent agreement with measured values. This method reduces the uncertainties of a factor of about 2 for the AP-8 MIN/MAX models to less than 30%.