Synchrotron powder diffraction patterns and Raman spectra of synthetic coffinite, USiO4, were collected for pressures up to 35 GPa and are complemented with DFT+U-based calculations. USiO4 undergoes a first-order phase transition from a zircon-type (space group I-41/amd) to a scheelite-type structure (space group I41/a) at approximate to 15 GPa and ambient temperature. Contrary to earlier reports, the data indicate that this transition is completely reversible upon pressure release. Bulk moduli were obtained from the pV data for the zircon-type and scheelite-type USiO4 phases. For zircon-type USiO4, the value for B = 186(5) GPa, whereas, for the scheelite-type phase, B = 204(9) GPa, where the latter is significantly lower than a value proposed earlier (B = 274(16) GPa, [Zhang, F. X.; et al. Am. Mineral. 2009, 94, 916]). Lattice dynamical calculations point toward a G-point soft mode triggering the pressure-induced phase transition

First-principles calculations have been employed to examine the possible use of electron energy loss spectroscopy (EELS) as a tool for determining the presence of OH groups and hence hydrogen content in compounds. Our density functional theory (DFT) based calculations describe accurately the experimental EELS results for forsterite (Mg2SiO4), hambergite (Be2BO3(OH)), brucite (Mg(OH)2) and diaspore (α-AlOOH). DFT calculations were complemented by an experimental time resolved study of the oxygen K-edge in diaspore. The results show unambiguously that there is no connection between a pre-edge feature in the oxygen K-edge spectrum of diaspore and the presence of OH groups in the structure. Instead, the experimental study shows that the pre-edge feature in diaspore is transient. It can be explained by the presence of molecular O2, which is produced as a result of the electron irradiation.

The theoretical investigation of the Fermi surface (FS) and constant-energy one near the Fermi energy of La2−xSrxCuO4 and YBa2Cu3O7 is the aim of this work.

Density functional theory can be used to interpret and predict spectroscopic properties of solid-state materials. The relevant computational solutions are usually available in disparate DFT codes, so that it is difficult to use a consistent approach for analyzing various spectroscopic features of a given material. We review the latest developments that are aimed to provide a collection of analytical tools within one DFT package, CASTEP. The applications covered include core-level EELS, solid-state NMR, optical properties, IR and Raman spectroscopy. We present also results of the EELS analysis of NbO and Nb2O5 that show the first published example of CASTEP spectra from d-states. Raman activities calculated for a test set of small molecules and the convergence requirements for such calculations are discussed.

Energy loss spectra from a variety of cubic oxides are compared with ab-initio calculations based on the density functional plane wave method (CASTEP). In order to obtain agreement between experimental and theoretical spectra, unique material specific considerations were taken into account. The spectra were calculated using various approximations to describe core-hole effects and electron. The calculations are based on both the generalized gradient approach and the local spin density approximation when dealing with the correlation to show qualitative agreement with the sensitive oxygen K-edge spectra in ceria, zirconia, and urania. Comparison of experimental and theoretical results let us characterize the main electronic interactions responsible for both the electronic structure and the resulting EELS spectra of the compounds in question.

The magneto-optical spectra of NiMnSb were calculated in the framework of the local spin density approximation (LSDA) combined with dynamical mean-field theory (DMFT). Comparing with results based on the plain LSDA, the additional account of many-body correlations via DMFT results in a noticeably improved agreement of the theoretical Kerr rotation and ellipticity spectra with corresponding experimental data.

Density functional calculations are used to investigate spin structure of quantum fluctuations (QF), low-lying excitations and their relationship to superconductivity in Sr2RuO4. It is shown how the presence of the Fermi surface nesting in this highly two-dimensional system leads in theory to establishment of antiferromagnetic spin density superstructure in the ground state and therefore in QF. Our calculations confirm the ground state spin structure which develops in Sr2RuO4 upon partial Ti substitution found in experiment, even at concentrations typical for doppants. The Ti disrupts the Ru-O-Ru chains, leading to an increase in the local density of states, and thereby favors moment formation oil the neighboring Ru sites. Supercell calculations and frozen spin wave calculations show a marginal antiferromagnetic instability at the Fermi surface nesting vector. At this wave vector, the magnetocrystalline anisotropy is found to be very small. The spin structure of QF and low energy excitations are discussed in relation to these results. The nesting leads to the following effects: (1) development of the spin Structure in QFs and related low-lying excitations as a result of enhancement of the intersite exchange, (2) effect of lasing on QFs, which implies selecting and amplifying waves out of the wave packet with nesting vector q(N) only. The crystalline strontium ruthenate can be viewed as a superconducting liquid crystal, since the triplet nature of superconductivity makes it close to symmetry-broken phases of He-3 liquid, whereas the spin and orbital moments are ordered on the scale of spin-spin correlation length. (c) 2005 Elsevier B.V. All rights reserved.

To explain the remarkable oscillations observed in the x-ray magnetic circular dichroic absorption spectra from Gd/Cu multilayers at the Cu K edge, ab initio calculations have been made using the fully relativistic Korringa-Kohn-Rostoker formalism including the spin-orbit coupling. The result reproduces well the oscillatory profiles in the near-edge region, but the peaks and valleys do not correspond to those in the difference density of states [Formula: see text] for the unoccupied Cu 4p band above the Fermi level. We find small spin and orbital moments on the interfacial Cu sites, which decay towards the core of the Cu layer. Surprisingly, neither the spin nor the orbital moments die out on the Cu sites four atomic layers away from the Co interface. This extended polarization is ascribed to the hybridization of the Cu 4p and the Gd 5d states. The accuracy of the calculation is supported by the near-bulk spin and orbital moments found on the Gd sites away from the interface.

We present a charge and self-energy self-consistent computational scheme for correlated systems based on the Korringa-Kohn-Rostoker (KKR) multiple scattering theory with the many-body effects described by the means of dynamical mean field theory (DMFT). The corresponding local multi-orbital and energy dependent self-energy is included into the set of radial differential equations for the single-site wave functions. The KKR Green's function is written in terms of the multiple scattering path operator, the later one being evaluated using the single-site solution for the t-matrix that in turn is determined by the wave functions. An appealing feature of this approach is that it allows to consider local quantum and disorder fluctuations on the same footing. Within the Coherent Potential Approximation (CPA) the correlated atoms are placed into a combined effective medium determined by the dynamical mean field theory (DMFT) self-consistency condition. Results of corresponding calculations for pure Fe, Ni and Fe_xNi_1-x alloys are presented.

Spin-density functional calculations are used to investigate the proximity to antiferromagnetism and the effects of partial Ti substitution in Sr2RuO4. Ti is found to enter the lattice as Ti4+ with only a small relaxation of the neighboring O ions. The Ti disrupts the Ru-O-Ru chains, leading to an increase in the local density of states, and thereby favors moment formation on the neighboring Ru sites. Supercell calculations and frozen spin-wave calculations show a weak antiferromagnetic instability at the Fermi surface nesting vector implying nearness to a quantum critical point. Properties of Sr2RuO4 are discussed in relation to these results.

AbstractFor Abstract see ChemInform Abstract in Full Text.

We report results on calculations of the electronic, magnetic and transport properties of Fe/GaAs and Fe/Ge multilayer systems. On the base of the generalized Bloch theorem we have calculated the electronic structure for a set of spin‐spiral structures, which allows us to extract averaged interlayer exchange parameters and their dependence on the width of the semiconductor spacer. The dependence of the dc conductivity and magnetoresistance on the width of the semiconductor layer and the relative angle between the moments of adjacent FM‐layers allowed us to model the dependence of the resistivity on a magnetic field. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The influence of dynamical correlation effects on the magneto-optical properties of ferromagnetic Fe and Ni has been investigated. In addition the temperature dependence of the self-energy and its influence on the DOS and optical conductivity is considered. Magneto-optical properties were calculated on the basis of the one-particle Green's function, which was obtained from the DMFT-SPTF procedure. It is shown that dynamical correlations play a rather important role in weakly correlated Fe and substantially change the spectra for moderately correlated Ni. Magneto-optical properties obtained for both systems are found in better agreement with experiment than by conventional LDA calculations.

An approach for the calculation of the optical and magneto-optical properties of solids based on the one-particle Green function is introduced in the framework of the linear muffin-tin orbital method. The approach keeps all advantages of the more accurate Korringa-Kohn-Rostoker scheme as the possibility to account for many-body effects in terms of the nonlocal energy dependent self-energy but is numerically much more efficient. Application of various proposed model self-energies for the calculation of the optical properties of bulk Ni and Fe demonstrates the great potential of the new scheme.

An incorporation of the LDA+U formalism into the spin-polarized relativistic Korringa–Kohn–Rostoker (SPR-KKR) method of band-structure calculations is presented. This new approach accounts for one-particle relativistic effects in a proper way when applying the LDA+U method to get an improved description of correlation effects compared to plain LDA-based calculations. In addition, it allows to deal with disordered systems in a straight forward manner by a combination with the coherent potential approximation (CPA) alloy theory. These features are demonstrated by results obtained for fictitious ferromagnetic fcc-Uranium and the disordered alloy system FexCo1−x.

The LDA+U method is used to calculate exchange integrals in strongly correlated cuprate compounds. We distinguish two approaches. The first one compares directly the total energies of different collinear spin arrangements with the corresponding ones of Heisenberg-like models. The second approach maps the energy of noncollinear spin-spiral states to the mean-field solutions of the effective spin Hamiltonian. Both approaches are applied to Sr2CuO2Cl2 which can be described with good accuracy by a two-dimensional Heisenberg model with only nearest-neighbor exchange. It is shown that the consideration of quantum fluctuations improves the resulting exchange integrals. The variation of the results with U and the difference between the two approaches are small. Both methods have also been applied to Ba2Cu3O4Cl2 which has two coupled antiferromagnetic spin systems. The coupling between the two subsystems has been shown to be larger than previously estimated.

The magnetoresistance due to a domain wall in pure Fe was studied theoretically by means of ab initio electronic structure calculations based on a linear muffin-tin orbital method modified for noncollinear magnets. The Bloch walls were modeled by a superlattice structure in the (001) direction of the bcc lattice with alternating regions of collinear and spiral-like magnetizations. The conductivity was calculated by means of the linearized Boltzmann equation in a relaxation time approximation. The magnetoresistance due to a domain wall (DW) is presented as a function of the angle between the magnetizations, domain-wall thickness, and domain size. The orientation dependence of the magnetoresistance due to a DW in pure Fe has cos-like behavior in contrary to the giant magnetoresistance in Fe/Cr superlattices. It was also shown that the presence of Cr increases the GMR amplitude in comparison with pure Fe separated by a noncollinear domain wall of equal size. The Kronig-Penney model was used in order to show that the oscillations of GMR as a function of domain size stem from quantum well states crossing the Fermi level.

TlTaS3 was prepared by applying a sequence of two melting processes with mixtures of Tl2S, Ta, and S having different molar metal to sulphur ratios. TlTaS3 crystallises in space group Puma with a = 9.228(3) Angstrom, b = 3.5030(6) Angstrom, c = 14.209(3) Angstrom, V = 459.3(2) Angstrom(3), Z = 4. The structure is closely related to the NH4CdCl3-type. Characteristic features of the structure are chains of edge-sharing [Ta(+5)S4S2/2](2) double octahedra running along [010]. These columns are linked by Tl+ ions. The Tl+ ion is surrounded by eight S2- anions to form a distorted bi-capped trigonal prism. The Tl+ ions are shifted from the centre of the trigonal prism toward one of the rectangular faces. This is discussed in context with other isostructural compounds. TlTaS3 is a semiconductor. The electronic structure is discussed on the base of band structure calculations performed within the framework of density functional theory.

The electronic and magnetic properties of ferromagnet-semiconductor (FM-SC) heterostructure systems have been studied by means of scalar-relativistic KKR-CPA band structure calculations. As a structural model for our calculations periodic multilayer systems have been assumed, taking for the ferromagnet Fe and for the semiconductor GaAs. A justification for the applicability of this geometrical model in describing the electronic and magnetic properties of the real Fe-GaAs-Fe trilayer system is given. Making use of the Coherent Potential Approximation (CPA), the influence of interdiffusion at the Fe-GaAs interface within the multilayer system has been investigated in addition. On the basis of the electronic structure calculations, the magnetic circular X-ray dichroism (MCXD) has been investigated for the L-3-edges absorption spectra of Ga and As in the near-edge regime (XANES). In both cases the MCXD signal was found to be pronounced enough to be detectable and should motivate corresponding experimental studies.