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ELECTRONIC-STRUCTURE OF THE GAMMA'+GAMMA PHASE IN NICKEL-BASED SUPERALLOYS

JOURNAL OF PHYSICS F-METAL PHYSICS 1988年第8期18卷 1839-1847页

作者： CAO, J LIU, FS WANG, CY CENT IRON & STEEL RES INST DEPT 2BEIJINGPEOPLES R CHINA

The electronic structure of Mg-reinforced nickel-based superalloys has been studied. By setting up models for the mechanism of Mg in nickel-based superalloys, the local density of states, charge transfer, structural energy, and Fermi level of the systems have been calculated with Haydock\'s recursion method (1972, 1975). The difference in structural energy of clusters including Mg and its neighbours in between systems in model I and model II shows that Mg prefers and stabilises gamma \' phases. The amount of charge transfer of Mg in the gamma \' phase of a nickel-based superalloy indicates that Mg tends to enter a gamma \' phase.

关键词： charge transfer Density of states recursion method Electronic structure superalloys Neighbor Magnesium gamma phases Fermi level Phase Nickel base superalloys

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The extended algebra of the minimal models

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NUCLEAR PHYSICS B 2007年第3期776卷 365-404页

作者： Mathieu, Pierre Ridout, David Univ Laval Dept Phys Quebec City PQ G1K 7P4 Canada

The minimal models M(p', p) with p' > 2 have a unique (non-trivial) simple current of conformal dimension h = 1/4(p' - 2)(p - 2). The representation theory of the extended algebra defined by this simple current is investigated in detail. All highest weight representations are proved to be irreducible: There are thus no singular vectors in the extended theory. This has interesting structural consequences. In particular, it leads to a recursive method for computing the various terms appearing in the operator product expansion of the simple current with itself. The simplest extended models are analysed in detail and the question of equivalence of conformal field theories is carefully examined. (c) 2007 Elsevier B.V. All rights reserved.

关键词： QUANTUM-FIELD THEORY GRADED PARAFERMIONS OPERATOR ALGEBRA MONOMIAL BASIS BASES recursion method Minimal quantum field theory OPERATOR PRODUCT EXPANSION conformal theories Algebra arithmetic operator

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ELECTRONIC-STRUCTURE AND MAGNETIC-PROPERTIES OF Y-CO, Y-FE AND Y-MN INTERMETALLIC COMPOUNDS

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JOURNAL OF PHYSICS F-METAL PHYSICS 1985年第7期15卷 1511-1524页

作者： INOUE, J SHIMIZU, M Dept. of Appl. Phys. Nagoya Univ. Japan

Electronic densities of states in Y-Co (Y2Co17, YCo5, Y2Co7 and YCo3), Y-Fe (Y2Fe17, Y6Fe23 and YFe3) and Y6Mn23 intermetallic compounds are calculated in the tight-binding d-band model by making use of the recursion method. The average and local magnetic moments on Co and Fe atoms, the high-field susceptibility and the coefficient of the low-temperature specific heat are calculated and compared with the experimental values. The temperature dependences of the spin susceptibility and the spontaneous volume magnetostriction in Y-Fe compounds are also calculated and compared with the experimental results.

关键词： Magnetic moment recursion method Andromeda Electronic structure cobalt volume magnetostriction Spin susceptibility carbon monoxide Intermetallic compounds Magnetic properties Electronic density of states Coefficients

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ELECTRONIC-STRUCTURE AND PHASE-STABILITY OF A15 TRANSITION-METALS AND ALLOYS

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JOURNAL OF PHYSICS F-METAL PHYSICS 1983年第12期13卷 2543-2567页

作者： TURCHI, P TREGLIA, G DUCASTELLE, F UNIV PIERRE & MARIE CURIE DYNAM RESEAU & UITRA SONS LABF-75005 PARISFRANCE UNIV PARIS 11 PHYS SOLIDES LABF-91405 ORSAYFRANCE

The authors study the electronic structure and the stability of A15 transition metals and alloys at 0K, using a tight-binding approximation and the recursion method. The band contribution to the energy is shown to favour the A15 structure for pure metals when the number of d electrons is about four. This is in agreement with some experimental observations concerning W, Nb, and Cr. Then the energy of formation and the ordering energy of A15 compounds are calculated. They are shown to be quite similar to those of other comparable ordered structures such as the Cu3Au (L12) structure. The relative stability of the A15 and L12structures is studied in some detail. A15 and L12are found to be stable for small and large values of the mean number of d electrons respectively, as is observed experimentally. Finally a general theoretical structural map is presented which accounts for many observed A3B transition compounds.

关键词： recursion method Electronic structure energy of formation METAL ALLOY ordering energy Phase stability transition metal TSPAN7 gene electron beam Transition Elements pure metals

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CALCULATION OF ELECTRONIC DENSITY OF STATES FOR AMORPHOUS ZRCU AND ZRNI ALLOYS

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JOURNAL OF PHYSICS F-METAL PHYSICS 1985年第2期15卷 287-296页

作者： FROTAPESSOA, S Inst. de Fisica Sao Paulo Univ. Brazil

The author has recently developed a simple scheme based on the recursion method which allows the relative position of the d bands in an amorphous transition-metal alloy to be determined if the average charge transfer is known. To find the hopping integrals the author uses tabulated values of the overlap parameters (dd sigma , dd pi , and dd delta ) obtained from a fit to the bands of the pure metals. This scheme allows a parameterized Hamiltonian to be built to represent the transition-metal alloys, avoiding the need for a detailed fitting of LCAO bands to the bands of a corresponding crystalline compound. In the procedure the overlap parameters are tabulated for the pure metal and charge transfer is either known or neglected. Therefore the results obtained for the density of states of the alloy are well defined and parameter free. Here the author uses the above procedure to obtain the electronic structure of amorphous ZrCu ( alpha -ZrCu) and alpha -ZrNi alloys for two different compositions. The results are compared with those obtained by other methods and with experiment. The calculations are in good agreement with existing UPS and XPS results for these alloys. The values obtained for the density of states at the Fermi level, N(EF), for alpha -ZrCu are also compatible with those inferred from experimental data for melt-spun samples.

关键词： charge transfer Density of states recursion method METAL ALLOY Bands Writers Countries (nations) Transition metal alloys noncrystalline Electronic density of states Bands and orchestras pure metals

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Selective hydrogenation of CO on Fe₃S₄{111}: a computational study

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FARADAY DISCUSSIONS 2017年第0期197卷 325-336页

作者： Roldan, Alberto de Leeuw, Nora H. Cardiff Univ Sch Chem Main BldgPk Pl Cardiff CF10 3AT S Glam Wales

Fischer-Tropsch (FT) synthesis has been a recursive method to form valuable molecules from syngas. Metal surfaces have been extensively studied as FT catalysts;among them, iron presents several phases under reaction conditions, oxides and carbides, as active sites for the FT and reverse water gas shift reaction. We present CO reduction on an iron sulfide phase with spinel structure, Fe3S4, also considering the pathways where C-O dissociates leaving CHx species on the surface, which may feed longer aliphatic chains via the FT process. We analysed the thermodynamic and kinetic availability of each step leading to O and OH species co-adsorbed on the surface as well as the formation of H2O from the hydrogenation of the alcohol group in the molecule. This detailed analysis led to energy profiles on both active sites of the surface, and we conclude that this Fe3S4 surface is highly selective towards the formation of methanol, in full agreement with experimental results. These findings point out that the C-C bond formation on greigite takes place through a hydroxycarbene FT mechanism.

关键词： Bond formation recursion method greigite Water gas shift reaction ALCOHOL GROUPS Active Site Iron Phase Hydrogenation

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Site dilution of quantum spins in the honeycomb and square lattices

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PHYSICA B-CONDENSED MATTER 2006年第SPEC. ISS.期378-80卷 137-138页

作者： Castro, Eduardo V. Peres, N. M. R. Univ Porto CFP Fac Ciencias P-4169007 Oporto Portugal Univ Porto Dept Fis Fac Ciencias P-4169007 Oporto Portugal Univ Minho GCEP Ctr Phys P-4710057 Braga Portugal Univ Minho Dept Fis P-4710057 Braga Portugal Boston Univ Dept Phys Boston MA 02115 USA

The effect of site dilution on the magnetization and oil the density of states (DOS) of a spin-S antiferromagnetic Heisenberg-model in the honeycomb lattice is studied using linear spin wave theory. For a given value of dilution the linearized Hamiltonian is solved in real space. The DOS is computed using a modified version of the recursion method, usually used for fermionic systems. The finite-size scaling results for the magnetization in the Honeycomb lattice are in qualitative agreement with similar results obtained for the square lattice case. We apply our results to the description of dilution effects on the Neel temperature of MnpZn1-pPS3, a spin 2\5 Heisenberg antiferromagnet in an honeycomb lattice. (c) 2006 Elsevier B.V. All rights reserved.

关键词： Heisenberg model dilution honeycomb antiferromagnetism spin waves recursion method

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Tight-binding recursion calculations of step energetics on the GaAs(110) surface

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JOURNAL OF CHEMICAL PHYSICS 1997年第15期107卷 5914-5917页

作者： Kang, HC Chen, XF Tan, HS Department of Chemistry National University of Singapore 10 Kent Ridge Crescent Singapore 119260

On the GaAs(110) surface steps perpendicular to the [001] direction may be either arsenic-terminated or gallium-terminated. We, compute the energy difference between these steps using a tight-binding recursion method. We find that the arsenic-terminated step is more stable by approximately 0.5 eV. Our results suggest that some recent experimental observations on the shape of islands formed during homoepitaxy on CaAs(110) may be the consequence of an energy-driven rather than a kinetics-driven epitaxial growth. (C) 1997 American Institute of Physics.

关键词： gallium arsenide III-V semiconductors recursion method surface phonons dangling bonds

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Research of the behaviour of O chemisorption on the (110) surface of Rh_x-Pt_1-x alloy

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CHINESE PHYSICS 2006年第3期15卷 641-644页

作者： Zhang, H Zhang, GY Wang, RD Zhong, B Shenyang Normal Univ Coll Phys Sci & Technol Shenyang 110034 Peoples R China

An atomic group model of the disordered binary alloy Rh-x-Pt1-x has been constructed to investigate surface segregation. According to the model, we have calculated the electronic structure of the Rh-x-Pt1-x alloy surface by using the recursion method when O atoms are adsorbed on the Rh-x-Pt1-x(110) surface under the condition of coverage 0.5. The calculation results indicate that the chemical adsorption of O changes greatly the density of states near the Fermi level, and the surface segregation exhibits a reversal behaviour. In addition, when x < 0.3, the surface on which O is adsorbed displays the property of Pt;whereas when x > 0.3 it displays the property of Rh.

关键词： chemisorption surface segregation recursion method density of states

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On a quantum plateau of magnetization in metal-organic quasi-one-dimensional ferrimagnets

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JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 2003年第3期97卷 615-623页

作者： Bostrem, IG Boyarchenkov, AS Konovalov, AA Ovchinnikov, AS Sinitsyn, VE Ural State Univ Ekaterinburg 620083 Russia

The possibility of realizing a quantum plateau of magnetization in [Mn(hfac)(2)BNOR] metal-organic compounds is investigated theoretically. A model of a one-dimensional ferrimagnetic chain (5/2, 1) is used for calculating the magnetization as a function of an external field by the method of discrete path integral representation (DPIR). Within this model, the coexistence of classical and quantum plateaus of magnetization is revealed. It is shown that the critical field H-c1 that destroys the classical plateau (ground-state magnetization) is determined by the optical gap in zero field, which is estimated by the matrix-product method and a numerical method of exact diagonalization (recursion method). (C) 2003 MAIK "Nauka / Interperiodica".

关键词： diagonalization recursion method external electric field magnetization Numerical methods Critical field Prerubral field quanta Curvilinear integral OPTICAL GAP plateaus annonacin-A-one

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