Magnetosensitive reactions in ionic crystals during their plastic deformation

A new method for investigating spin-independent chemical reactions between radical centers at point defects and dislocations in solids is proposed. The method is based on studying the mobility of dislocations in a field of mechanical stresses. The application of a magnetic field with inductionB=1 T results in a change in the state of the defects of the crystal lattice in ionic crystals, which can be observed a long time (up to 10³ s) after switching off the field. Radical reactions were analyzed in which the kinetics of changes in the magnetic field can cause the effect of magnetic “memory” in distorted microregions of the lattice. Translated fromIzvestiya-Akademii Nauk Seriya Khimicheskaya, No. 4 pp. 739–744, April. 1997.     

Composition and structure refinement of superconducting crystals Y1? x Tb x Ba2Cu3O6+δ ( x = 0.10; δ = 0.75)

Crystals of Y_0.90Tb_0.10Ba₂Cu₃O_6.75 have been prepared by spontaneous crystallization from slowly cooled non-stoichiometric melt of the system Y-Tb-Ba-Cu-O. Average size of platelet crystals having mirror surface is 2×2, the largest — 8×9 mm with thickness 0.1–0.2 mm. The crystals have been characterized by powder X-ray diffraction and electron microprobe analysis. Tetragonal symmetry of the crystals has been determined by X-ray diffraction. Magnetic susceptibility measurements have revealed that the crystals manifest transition to superconducting state without additional annealing (T _c = 60 K). Structures and compositions — Y/Tb ratio (σ = 0.01) and oxygen content (σ = 0.04) — have been refined for two single crystals. Possibility of rhombic distortion of the tetragonal symmetry is discussed. __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 6, pp. 1101–1107, November–December, 2008. Original Russian Text Copyright ? 2008 by L. P. Kozeeva, N. V. Podberezskaya, N. V. Kuratieva, M. Yu. Kamaneva, and A. G. Blinov     

Soliton model of electron transfer in mixed-valence dimers and trimers

The soliton approximation is examined for mixed-valence dimers and trimers with one migrating electron. The calculations use Hamilton's canonical equations and a time-dependent wave function of the soliton type. In the two limiting cases (strong and weak vibronic coupling), the soliton approximation correlates well with the exact analytical solution. As in the adiabatic approximation at g²/v=1, the delocalized limit (quasifree electron) is transformed to the localized one (electron locked on the center). For molecular trimers, the soliton approximation allows us to reveal the cases where the transfer of an electron from the first to the third center is accompanied by electron density concentration on the intermediate center. Institute of Chemistry, Academy of Sciences, Moldova Republic. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 6, pp. 46–53, November–December, 1994. Translated by L. Smolina     

Vitrification and structural differences between metal glass,quasicrystal, and Frank-Kasper phases

The concept of icosahedral short-range order is extended to metallic glass, quasicrystal, and Frank-Kasper phases. The cluster model, together with the theory of local structural fluctuations, explains the static elasticity of glass, which distinguishes glass from liquid. An elastic peak of the dynamic structural factor indicates the possibility of transverse mode propagation in glass. As opposed to dislocations and disclinations in crystals, those in glass are artificially introduced defects, which serve as easily perceptible structural models. Thermodynamic relaxation theory may only be used for limited groups of vitrifying compounds the same applies to representation of vitrification as the second-order phase transition. The structure of real quasicrystals may not be adequately represented by Penrose tiling even after its decoration. This is associated with packing defects, inclusions of other phases, and chemical inhomogeneities. Quasicrystals have specific defects in an icosahedrally coordinated network of bonds, which distinguish them from Frank-Kasper phases. Criteria for isolating physically realizable Penrose tiling from all possible mosaics of this type are suggested. Structural distortions that transfer the diffraction rings of quasicrystalline samples into ellipses are explicable even in a linear approximation for the stress field created by a phason. The term “long-range order” seems to be wrong even for ordinary crystals. For quasicrystals, the notion of “rotational” order is more pertinent. Institute of Thermal Physics, Ural Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 138–158, January–February, 1996. Translated by L. Smolina     

Prephase state in 2-bromo-2-nitropropane-1,3-diol crystals: Structural aspects and IR spectra

This paper is a continuation of our series of publications dealing with crystal-lattice processes occuning on heating and at temperatures near the transition point and accompanied by structural changes in discrete molecules and in the crystal structure as a whole. The prephase state of 2-bromo-2-nitropropane-1,3-diol crystals and the transition from monoclinic to cubic phase are studied by IR spectroscopy at 296–391 K. Translated fromZnumal Strktumo, Chimii, Vol. 41, No. 2, pp. 294–299, March–April, 2000.     

New Method for calculating effective charges on atoms in molecules, clusters, and solids

A procedure for calculating effective charges on atoms in an arbitrary polyatomic system has been developed on the basis of the one-electron DV cluster method. Effective charges are calculated as three-dimensional integrals of electron density over the space around atomic nuclei in the object under investigation. An original procedure is suggested to assign the charge density to a particular center at every point of space. Translated fromZhurnal Struktumoi Khimii, vol. 39, no. 6, pp. 1134–1140, November–December, 1998.     

Setting the boundary conditions by the potential shift in the self-consistent field (Xα-scattered wave) cluster calculations

Potential shifts given by the Madelung potentials in different regions of a molecular cluster are determined in the MT approximation. Nickel and zinc oxides are employed to consider the interrelation between the approaches to the calculation of the boundary conditions in terms of the Watson sphere and the potential shift in the cluster calculations of perfect and imperfect ionic crystals using the self-consistent field (Xα-scattered wave) method. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 1, pp. 23–31, January–February, 1997. Original article submitted February 12, 1996.     

Embedded cluster calculation of the Ce3+ impurity in Lu2SiO5 crystals including crystal lattice relaxation and polarization

Results of electronic structure studies of the Ce³⁺ impurity in Lu₂SiO₅ crystals allowing for lattice polarization and relaxation are given. The calculations were performed by the embedded cluster method combining the scattered wave and molecular static methods. The effect of lattice deformation induced by the defect on the results of calculations is discussed. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 6, pp. 1046–1052, November–December, 1997.     

Magnetic vacancies, ordering, and properties of bismuth-substituted rare-earth ferrite garnets

Thermodynamic analysis of the garnet formation processes and crystal chemical simulation of the filling of a garnent crystal lattice with cations were used to identify the types of defects and to estimate their numbers and contributions to the magnetic properties of bismuth-substituted rare-earth scandium-containing ferrogallogarnets. The effective magnetic moments of the garnets were calculated with allowance for the HS- and LS-states of paramagnetic ions. A classification of crystal defects was proposed. Principles and postulates suitable for any multisublattice and multicomponent crystals were formulated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1040–1048, June, 1999.     

Three-level model of defect accumulation during ice formation from liquid water

A mechanism of formation of nonequilibrium point defects in ice in the course of water crystallization is suggested. The mechanism takes into account differences between the energy structures of ice and water as well as diffusion, thermal generation, and relaxation of defects. Analytical relations are obtained; these relations show that at higher rates of crystallization the concentration of defects in ice increases to the value of equilibrium density of defects in water. Some defects are withdrawn to the liquid phase and accumulate before the crystallization front. The efficiency of defect withdrawal is maximal at low rates of crystallization. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 3, pp. 511–515, May–June, 1997.     

A new method to calculate overlap integrals of vibrational wave functions in the theory of vibronic spectra of polyatomic molecules

An approximate method to calculate overlap integrals of vibrational wave functions of combined electron states is proposed. It uses reducibility of the general transformation of normal coordinates and quasiorthogonality of the Dushinsky matrix. Simple analytical expressions and convenient recurrent relations for the desired integrals of Franck-Condon and Herzberg-Teller types are found. The errors of calculation are of the same order as those of the existing “accurate” methods (≤5%), and the speed of calculation is higher by more than two orders. The study was carried out under financial support of the Russian Fundamental Research Fund (93-02-3405). K. A. Timiryazev Moscow Agricultural Academy. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 2, pp. 16–23, March–April, 1994. Translated by L. Chernomorskaya     

Application of the Colle–Salvetti model to the uniform electron gas

An application of the Colle–Salvetti wave function (Colle and Salvetti in Theor Chim Acta 37: 329, 1975) to the uniform electron gas model is made. Some different levels of approximation are used. Contrarily to the previous conclusions of other work (Tao et al. in Phys Rev A 63: 032513, 2001), the present result shows that the Colle–Salvetti wave function is able to reproduce, to a semiquantitative level, the properties of the uniform electron gas. The most important request for this result is an apropiate choice for the value of the only parameter entering in the Colle–Salvetti wave function. The present results are a good complement to those obtained by Moscardó et al. (Theor Chem Accounts 115: 334, 2006) for atoms. On the basis of the results obtained in this paper, a very simple functional for the correlation energy is put forward. Its application to the uniform electron gas, lead to a very reasonable set of results. It can be concluded that the Colle–Salvetti wave function remains being a good option to built, in an approximate way, the correlation component of a N-electron system. Contribution to the Serafin Fraga Memorial Issue.     

Fragment calculation of electronic structures of polyatomic molecules in the ground state. I. A method of intermediate fragment

A method is proposed for fragment calculation of electronic structures of polyatomic molecules in the ground state. The wave function of a molecule in the ground state in single-determinantal representation of a closed shell is employed. The concise formulation allows efficient calculation of the electronic structures of polyatomic molecules taking into account possible charge transfer between interacting molecular fragments. V.I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Translated fromZhurnal Struktumoi Khimii, Vol. 36, No. 3, pp. 387–394, May–June, 1995. Translated by I. Izvekova     

Orthogonal contacts between benzene rings: A special type of specific intermolecular interactions

The crystal structures of benzene and some of its derivatives are analyzed in detail. The structures are characterized by orthogonal contacts between the benzene cycles (OBzC). Although the orthogonal contacts conflict with the close packig law, they are an important structure-forming factor, being thus a specific type of intermolecular interactions. The OBzC system, which is inherent in the orthorhombic crystals of benzene, remains invariable in 2-aminophenol and 2-amino-4-chlorophenol crystals, notwithstanding other specific interactions (H-bonding and halogen...halogen contacts). OBzC are also observed in para- and ortho-cresol crystals. A classification of OBzC is given, and an especially effective projection method (rectangular projection) is suggested. M. V. Lomonosov Moscow State University, Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 5, pp. 775–789, September–October, 1995. Translated by L. Smolina     

Structural and orientational instability of crystals during their growth

Spontaneous long-range disorder arising from autodeformation defects during crystal growth is considered. Crystal chemical factors governing internal growth strains, which are the motive force of autodeformations, are discussed. Main tendencies in the development of autodeformation defects depending on growth conditions and crystal chemical structures are revealed. St. Petersburg State University. Translated fromZhurnal Struktumoi Khimii, Vol. 35, No. 5, pp. 50–59, September–October, 1994. Translated by L. Smolina     

On the theory of electronic structure of crystal surfaces

Electron wave functions are calculated for a system of two onedimensional atomic chains to illustrate the application of the modified tight binding equation method. A transfer of the local density of electronic states (LDES) from terminal to internal atoms of the chains, the effect of the emergence of the local state on LDES, and the variation of occupancy as a function of energy depending on the position of the atom relative to the end of the chain are discussed. In the limiting case of noninteracting chains, changes in LDES due to adsorption of the atom on the chain are considered. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 5, pp. 825–833, September–October, 1997.     

Equations of structure for valent crystals and the local valency balance

Physical principles underlying the local valency balance rule are discussed. It is shown that crystal stability does not obey the rule. Some more general rules of valent crystal structures are considered, and the corresponding equations, including Pauling's rules for one-aniont crystals as a particular case, are given. The equations may be used for analyses and predictions of complex structures. St. Petersburg State Technical University. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 4, pp. 717–723, July–August, 1995. Translated by L. Smolina     

Chemical bonding in LaFeAsO, SrFe2As2, and LiFeAs: Basic phases of new 18–56 K superconductors

Based on FLAPW-GGA calculations, a comparative study of the features of interatomic interactions in LaFeAsO, SrFe₂As₂, and LiFeAs layered crystals (basic phases of new 18–56 K superconductors) is carried out. Original Russian Text Copyright ? 2009 by I. R. Shein and A. L. Ivanovskii __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 3, pp. 573–576, May–June, 2009.