We present ab initio investigation of the electronic structure and magnetic properties of uranium monochal-cogenides: US,
USe, UTe. The calculations were performed by using the recently developed LDA+U+SO method in which both Coulomb and spin-orbit interactions have been taken into account in rotationally invariant form.
We discuss the problem of choice of the Coulomb interaction value. The calculated [111] easy axes agree with those experimentally
observed. The electronic configuration 5f3 was found for all uranium compounds under investigation. 相似文献
Implicit Runge-Kutta (RK) methods are in common use when addressing stiff initial value problems (IVP). They usually share the property of A-stability that is of crucial importance in solving the latter type of IVP. Radau IIA family of implicit RK methods is among the preferred ones. Especially its fifth-order representative named RADAU5 has received a lot of attention for use with lax accuracies. Here, we try the lesser possible perturbation of its coefficients. Then, we derive a trigonometric fitted modification that is intended to be applied in periodic IVPs. Numerical tests over a variety of problems with oscillatory solutions justify our effort. 相似文献
A crystal and magnetic structure of manganites Pr0.7Ca0.3Mn1?yFeyO3 (y = 0, 0.1) has been studied by means of powder neutron diffraction at pressures up to 4 GPa in the temperature range 15-300 K. Under high pressure, an appearance of A-type antiferromagnetic state in both systems was observed. Both compounds exhibit anisotropic compression of the lattice which leads to the apical compression of MnO6 octahedra along the crystallographic b-axis. The calculated from obtained structural data pressure dependence of the charge-carrier bandwidth is in a qualitative agreement with observed pressure behavior of insulator-metal transition temperature within the framework of the double-exchange model. 相似文献
Abstract The temperature dependences of the resistivity of La0.7Ca0.3Mn1?xFexO3 and La0.7Ca0.3Mn1?xFexO3 (0 < × < 0.04) mixed crystals were studied under hydrostatic pressures up to 15kbar. The substitution of Fe for Mn results in an increase of the resistivity and a continuous decrease of the metal-insulator transition temperature Tmi while the substitution of Ge for Mn leads to a more complicated Tmi(x)-curve. In all cases Tmi shifts under pressure with a rate between 1.6 and 2.9K/kbar and a correlation between Tmi and its pressure derivative dTmi/dP is observed which is in accordance with the general trend of dTmi/dP versus Tmi as derived for other manganites and is discussed in terns of a competition between superexchange and double exchange. 相似文献
First-principles calculations showed that the thermodynamic stability of β-based ordered η2-AlCu phase doped with Fe is due to iron substitution in the copper sublattice (FeCu), which corresponds to the maximum number of Fe–Al bonds in the first cubic coordination polyhedron. This iron localisation leads to stable ω-like atomic displacements and pentagonal Al-nets in the (010) plane of η2-AlCu(Fe). This phase with iron substituting copper (e/a?=?1.925) is an energetically preferred η-based non-canonical approximant of the icosahedral phase (e/a?=?1.86). The energy gain for the FeCu position is determined by strong covalent Fe3d–Al3p bonding, while there is a weak Fe3d–Cu4s3d hybridisation for the FeAl substitution. Using a composite cluster model, we demonstrate that short-range order in the pretransition state of the β-Al–Cu–Fe solid solution observed prior to the precipitation of η-phase is stabilised due to formation of Fe–Al bonds in the first cubic coordination polyhedron of the composite cluster. 相似文献
The electrooxidative polymerization of pyrrole on the surface of a glassy carbon electrode was studied, while varying the solvent, the type and concentration of supporting electrolyte, redox mediator addition to the polymerization medium, and hydrodynamic conditions. The efficiency of polymerization was determined as the ratio of the charge of the redox response of the polymer film under the standard conditions to the total charge of film formation in the monomer solution. The above factors were varied to determine the conditions that allow minimization of the ratio in order to obtain the highest yield of the polymer product. This was achieved by using a combination of a redox mediator addition with active stirring of solution.
The limit probabilities of the first-order properties of a random graph in the Erd?s–Rényi model G(n, n?α), α ∈ (0, 1), are studied. A random graph G(n, n?α) is said to obey the zero-one k-law if, given any property expressed by a formula of quantifier depth at most k, the probability of this property tends to either 0 or 1. As is known, for α = 1? 1/(2k?1 + a/b), where a > 2k?1, the zero-one k-law holds. Moreover, this law does not hold for b = 1 and a ≤ 2k?1 ? 2. It is proved that the k-law also fails for b > 1 and a ≤ 2k?1 ? (b + 1)2. 相似文献
A method for synthesis of new covalently linked spin-labeled cyclodextrin (CD) via the attachment of nitronyl nitroxide 2-(4-hydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl to permethylated β-cyclodextrin is described. Electron spin echo envelope modulation (ESEEM) studies demonstrate that the new spin-labeled CD exhibits dynamic equilibrium between conformations with radical fragment capping the cavity of CD and radical fragment located outside the cavity. In solution, nitronyl nitroxide attached to CD retains its sensitivity to nitric oxide (NO), as reaction with NO leads to formation of iminonitroxide fragment evidenced by continuous-wave (CW) electron paramagnetic resonance (EPR). At the same time, CW EPR study of the reaction with ascorbic acid shows that the described binding of nitronyl nitroxide to CD does not provide higher stability of radical towards the reduction, and the corresponding rate constants are close to those obtained for free nitronyl nitroxide. Plausible explanations of these observations are discussed. 相似文献
Two synthetic routes-ion-exchange preparation from layered Na(3)Ni(2)SbO(6) at 300 °C and direct solid-state synthesis at 1150 °C resulted in layered Li(3)Ni(2)SbO(6), a cation-ordered derivative from the rocksalt type. The Fddd form reported earlier could not be reproduced. According to the XRD Rietveld analysis, Li(3)Ni(2)SbO(6) is a pseudohexagonal monoclinic structure, C2/m, with a = 5.1828(2) ?, b = 8.9677(3) ?, c = 5.1577(2) ?, β = 109.696(2)°. No Li/Ni mixed occupancy was detected. At high temperatures, the magnetic susceptibility follows the Curie-Weiss law with a positive value of Weiss temperature, ~8 K, indicating a predominance of ferromagnetic interactions. However, Li(3)Ni(2)SbO(6) orders antiferromagnetically at T(N)~ 15 K. The effective magnetic moment is 4.3 μ(B)/f.u. which satisfactorily agrees with theoretical estimations assuming high-spin configuration of Ni(2+) (S = 1). Electron spin resonance (ESR) spectra show single Lorentzian shape line attributed to Ni(2+) ion in octahedral coordination. The absorption is characterized by isotropic temperature independent effective g-factor g = 2.150 ± 0.005. In accordance with the layered honeycomb crystal structure determined for Li(3)Ni(2)SbO(6), the superexchange interaction between Ni(2+) ions through Ni-O-Ni pathways within Ni(2)SbO(6) layers are assumed to be ferromagnetic, while the dominant interaction between layers is antiferromagnetic. 相似文献