Theoretical study of resonant x-ray emission spectroscopy of Mn films on Ag

We report a theoretical study on resonant x-ray emission spectra (RXES) in the whole energy region of the Mn $L_{2,3}$ white lines for three prototypical Mn/Ag(001) systems: (i) a Mn impurity in Ag, (ii) an adsorbed Mn monolayer on Ag, and (iii) a thick Mn film. The calculated RXES spectra depend strongly on the excitation energy. At $L_3$ excitation, the spectra of all three systems are dominated by the elastic peak. For excitation energies around $L_2$, and between $L_3$ and $L_2$, however, most of the spectral weight comes from inelastic x-ray scattering. The line shape of these inelastic ``satellite'' structures changes considerably between the three considered Mn/Ag systems, a fact that may be attributed to changes in the bonding nature of the Mn-$d$ orbitals. The system-dependence of the RXES spectrum is thus found to be much stronger than that of the corresponding absorption spectrum. Our results suggest that RXES in the Mn $L_{2,3}$ region may be used as a sensitive probe of the local environment of Mn atoms.Comment: 9 pages, 11 figure

Electronic structure and optical properties of TaC from the first principles calculation

Abstract.: The electronic and optical properties of tantalum carbide TaC have been calculated using the full-potential linearized augmented-plane-wave method within the local density approximation scheme for the exchange-correlation potential. We find that the optical spectra can be extremely sensitive to the Brillouin zone sampling. The influence of relativistic effects on the dielectric function is investigated. It is shown that the scalar-relativistic correction is much more important than spin-orbit coupling. Our results are found to be in good agreement with the available experimental data. The determinant role of a band structure computation with respect to the analysis of optical properties is discusse

Band Calculations for Ce Compounds with AuCu3_{3}-type Crystal Structure on the basis of Dynamical Mean Field Theory I. CePd3_{3} and CeRh3_{3}

Band calculations for Ce compounds with the AuCu$_{3}$-type crystal structure were carried out on the basis of dynamical mean field theory (DMFT). The auxiliary impurity problem was solved by a method named NCA$f^{2}$vc (noncrossing approximation including the $f^{2}$ state as a vertex correction). The calculations take into account the crystal-field splitting, the spin-orbit interaction, and the correct exchange process of the $f^{1} \rightarrow f^{0},f^{2}$ virtual excitation. These are necessary features in the quantitative band theory for Ce compounds and in the calculation of their excitation spectra. The results of applying the calculation to CePd$_{3}$ and CeRh$_{3}$ are presented as the first in a series of papers. The experimental results of the photoemission spectrum (PES), the inverse PES, the angle-resolved PES, and the magnetic excitation spectra were reasonably reproduced by the first-principles DMFT band calculation. At low temperatures, the Fermi surface (FS) structure of CePd$_{3}$ is similar to that of the band obtained by the local density approximation. It gradually changes into a form that is similar to the FS of LaPd$_{3}$ as the temperature increases, since the $4f$ band shifts to the high-energy side and the lifetime broadening becomes large.}Comment: 12 pasges, 13 figure

Model calculation of core level XPS spectra in early 3d-metal compounds

Using a configuration-interaction impurity-Anderson model we calculate core-hole X-ray Photoemission Spectra (c-XPS) for some early Transition Metal (TM) insulating compounds. Because in these compounds the valence (ligand) band is completely filled, the TM on-site Coulomb repulsion $U_{\rm dd}$ is treated exactly, as well as the 3d-core hole interaction $U_{\rm dc}$. The ground state of such a ligand-TM system with a nominally d$^0$ cation is described as a mixture of purely d$^0$ ionic state, and charge-transfer screened d$^1L$ and d$^2L^2$ states where $L$ denotes a hole in the ligand band. Our simplified model enables us to understand why c-XPS satellites are still present in CaF$_2$ or CaO, like in light TM compounds, but absent for KF compounds. In addition to $U_{\rm dd}$ and $U_{\rm dc}$, the other relevant parameters are the ligand-to-metal charge-transfer energy $\Delta$ and the corresponding hybridization $V$ (related to the metal-ligand transfer integrals). Finally quite a good fit to 2p$_{3/2}$-XPS of TiO$_2$ is obtained by using the parameter values estimated from (i) a LMTO band structure calculation of TiO$_2$, and (ii) another calculated fit of the K(Ti) pre-edge absorption spectrum in TiO$_2$.A l'aide du modèle d'impureté d'Anderson avec mélange de configurations, nous calculons les spectres X de la photoémission de cœur (c-XPS) pour certains composés isolants du début de la série des métaux de transition (MT). Comme la bande de valence de ces composés est complètement remplie, on peut traiter exactement la répulsion de Coulomb $U_{\rm dd}$ sur le site du MT ainsi d'ailleurs que l'interaction $U_{\rm dc}$ entre l'électron 3d et le trou de cœur. L'état de base d'un tel système contenant un cation de configuration d$^0$ est décrit par un mélange de l'état ionique purement d$^0$ et des états écrantés à transfert de charge d$^1L$ et d$^2L^2$ où $L$ est mis pour un trou dans la bande de valence. Ce modèle très simplifié est par exemple capable de comprendre pourquoi les satellites de la photoémission de cœur sont bien présents dans CaF$_2$ ou CaO, comme dans les composés de MT légers, mais absents dans les composés KF. En plus de $U_{\rm dd}$ et $U_{\rm dc}$, les autres paramètres pertinents sont $\Delta$, l'énergie de transfert de charge du métalloïde vers le métal et l'hybridation correspondante $V$ (reliée aux intégrales de transferts correspondantes). Aussi, nous avons pu obtenir un bon ajustement théorique du spectre 2p$_{3/2}$-XPS, mesuré dans TiO$_2$, et ceci en utilisant les valeurs des paramètres fournies par (i) un calcul de structure de bandes LMTO de TiO$_2$, (ii) un calcul des prépics du seuil K(Ti) d'absorption dans TiO$_2$

Electronic structure and optical properties of TaC from the first principles calculation

The electronic and optical properties of tantalum carbide TaC have been calculated using the full-potential linearized augmented-plane-wave method within the local density approximation scheme for the exchange-correlation potential. We find that the optical spectra can be extremely sensitive to the Brillouin zone sampling. The influence of relativistic effects on the dielectric function is investigated. It is shown that the scalar-relativistic correction is much more important than spin-orbit coupling. Our results are found to be in good agreement with the available experimental data. The determinant role of a band structure computation with respect to the analysis of optical properties is discussed

Chemical binding energies of point defects in palladium doped with hydrogen and d impurities

Using an extra-orbital model within a generalized « spd » tight-binding approximation, we calculate the chemical binding energy of a pair of hydrogen atoms in palladium within the infinite dilution limit; we find that clusters of hydrogen cannot form in accordance with inelastic neutron scattering data in α-palladium hydride. The strong repulsive interaction between a pair of hydrogen impurities at distance a, where a is the host lattice parameter, seems to be related to the presence of an intermediate metallic site between the two impurities. Also we determine the chemical binding energies between a hydrogen atom and d substitutional impurities and we discuss our results in relation with recent Mössbauer experiments. Finally we calculate the chemical binding energy between two d impurities in palladium which we compare with experimental data on the enthalpy of formation.Nous utilisons un modèle de type Friedel-Anderson dans l'approximation des liaisons fortes généralisées aux états s, p et d en vue de calculer l'énergie d'interaction chimique entre deux atomes d'hydrogène en dilution dans le palladium. Comme le montrent certaines expériences de diffraction inélastique de neutrons dans les hydrures α de palladium, nous trouvons aussi qu'il n'y a pas formation d'amas d'atomes d'hydrogène dans le palladium. La forte répulsion entre deux impuretés d'hydrogène à la distance a, où a est le paramètre de réseau, semble provenir de la présence d'un atome métallique situé entre les deux impuretés. Nous déterminons aussi les énergies chimiques d'interaction entre un atome d'hydrogène et différentes impuretés d substitutionnelles; nous discutons nos résultats en liaison avec de récentes expériences Mössbauer. Enfin nous calculons l'énergie d'interaction entre deux impuretés d en substitution dans le palladium et nous comparons cette énergie avec certaines données expérimentales sur l'enthalpie de formation