Electronic Structure Of Pd Research Articles

Positron annihilation studies on the electronic structure of Pd−Ag−H system

Angular Correlation of Annihilation Radiation (ACAR) is shown to be useful to examine the electronic structure of α-phase Pd1−yAgyHx system. Hydrogen absorption by Pd1−yAgy alloys results in the increase of both nearly free andd-localized electron numbers in compliance with the KKR-CPA calculation outcomes. The investigation of β-phase systems, PdHx hydrides as well as Pd1−yAgyHx materials, failed because of a high concentration of lattice defects.

Electronic structure of Pd(Ni)-noble metal alloys examined by positron annihilation

On the basis of a new method of treatment of angular correlation of annihilation radiation data there have been calculated the numbers NNF of nearly free- and N – NNF of d-localized-electrons as well as the positive ion core radii rc and interstitial electron densities nint for Pd1−xAgx, Pd1−xCux and Ni1−xCux alloys. The linear character of changes of N – NNF and nint with x reject the applicability of the rigid band model while the nint linearity confirms the electron redistribution model expectations. The values of the differences in rc and nint for pure metals are suggested to be the main reason for the different type of electronic structure of these alloys.

Densities of Interstitial Electrons in Pd(Ni)Noble Metal Alloys

AbstractThe ion core radii rc and interstitial electron densities nint for Pd, Ni, Ag, and Cu and for binary random alloys of these metals throughout the concentration ranges have been calculated on the basis of positron annihilation data. The differences in rc and nint for pure metals are suggested to be the main reason of different electronic structure of Pd–Cu and Pd(Ni)–Ag(Cu) alloys being the representatives of VCA and split‐band alloys, respectively.

Electronic Structure of Pd1−xNix Alloys Investigated by Positron Annihilation

AbstractThe entire concentration range of α‐phase Pd1−xNix alloys is studied by angular correlation and positron lifetime methods. The electron number per one alloy atom is analyzed and the progressive delocalization of d‐like electrons with increasing Ni concentration is postulated. Attention is also paid to the problem of annihilation rate in alloys. The changes in the character of annihilation parameter dependences on x are seemed to be connected with para‐ to ferromagnetic transition.

Electronic structure of small palladium and platinum clusters

Electronic structures of Pd 4 and Pt 4 clusters are studied using a model potential method in the Hartree-Fock-Roothaan scheme. The lowest bound state of Pd 4 is 3B 2 arising from (d 10) 3d 9s, while the ground state of Pt 4 is 7B 2, which comes from (d 9s) 4. Band structures of the clusters are compared with those of the bulk metals.

Angle-resolved photoemission and the electronic structure of Pd(111)

A theoretical study of various models which are commonly used for the analysis of angle-resolved photoemission is reported. For the example of the Pd(111) surface we discuss the quality and justification of these models. %e have calculated the @~I-resolved surface and bulk densities of states and the band structure of occupied and unoccupied states. FurtheHIlore, we have calculated photoemission spectra within the one-step approach. These theoretical spectra reproduce the main features and trends of the experimental data. We find that the k~I-resolved densities of states are, in general, not reflected in the photoemission. The spectra can only be interpreted in a modified direct-transition model where the inf1uence of the inelastic electron-electron interaction in the final state is taken into account.

Influence of relativistic contributions to the effective potential on the electronic structure of Pd and Pt

The influence of relativistic-interaction corrections to the energy density functional in the density functional formalism is examined using explicit calculations for Pd and Pt. We present and compare three separate self-consistent density-functional calculations which included (1) exchange only, (2) exchange and correlation, and (3) exchange and correlation plus relativistic-interaction corrections. Since they are of comparable or larger size, we have included and examined the effects of relativistic kinematics and non-muffin-tin potential shapes. Because the relativistic interaction corrections are significant only very near the nucleus, we report separately results for the core levels and for the valence states. The corrections obtained were negligible for Pd and small but significant for Pt.

A Calculation of the Electronic Structure of Palladium Containing an Impurity–Spin Paramagnetic Susceptibility

The electronic structure of Pd containing a substitutional impurity of a non-transition (Al and Si) or transition element (Ti, V, Zr, Nb, Mo, Ta and W) is calculated by using the KKR method. The results, when combined with an approximate expression for the spin susceptibility which takes account of the exchange enhancement, lead to a semiquantitative agreement with the experimental spin susceptibility data of Pd-based alloys.

Electronic structure of Pd: Compton scattering, soft-x-ray emission and x-ray photoelectron spectra

The electronic structure of Pd has been calculated in a self-consistent manner using the nonrelativistic augmented-plane-wave (APW) method and the Hedin-Lundqvist local-exchange-correlation approximation. Relativistic effects are discussed in terms of the relativistic Korringa-Kohn-Rostoker method for the self-consistent crystal potential. On the basis of the APW results theoretical intensities for the $L{\ensuremath{\beta}}_{2}$ emission spectrum and the Al-$K\ensuremath{\alpha}$ valence photoelectron spectrum have been calculated and are compared with results of previous experiments. Compton profiles for single-crystalline Pd have been measured and these are compared to the theoretical profiles, obtained from the APW crystal wave functions. In all cases the agreement with experiment is satisfactory.

ChemInform Abstract: SEMI‐EMPIRICAL SCF‐MO STUDIES OF PD(II)‐ AND HG(II)‐ETHYLENE COMPLEXES, THE OXYMERCURATION AND THE WACKER REACTION

Using the modified CNDO MO method, the electronic structures of Pd(II)- and Hg(II)-ethylene complexes have been studied successfully. Our MO calculations have shown that the nucleophilic attack of OH− on ethylene was accelerated by Pd(II) and Hg(II), and that the acceleration by Hg(II) was larger than that by Pd(II), these results agree well with those of the experiments. The cis-attack of OH− in the oxymercuration has also been discussed by the use of the results obtained by the MO calculations. The mechanism of the cis-type four-center addition of OH− to ethylene in the Wacker reaction, which was supposed by Henry and Jira et al. in spite of any direct evidence, has been supported by the MO calculations. Our calculations have been able to explain the Markovnikoff rule in the Wacker reaction and in the oxymercuration of propylene.

Semi-empirical SCF-MO Studies of Pd(II)- and Hg(II)-Ethylene Complexes, the Oxymercuration and the Wacker Reaction

Abstract Using the modified CNDO MO method, the electronic structures of Pd(II)- and Hg(II)-ethylene complexes have been studied successfully. Our MO calculations have shown that the nucleophilic attack of OH− on ethylene was accelerated by Pd(II) and Hg(II), and that the acceleration by Hg(II) was larger than that by Pd(II), these results agree well with those of the experiments. The cis-attack of OH− in the oxymercuration has also been discussed by the use of the results obtained by the MO calculations. The mechanism of the cis-type four-center addition of OH− to ethylene in the Wacker reaction, which was supposed by Henry and Jira et al. in spite of any direct evidence, has been supported by the MO calculations. Our calculations have been able to explain the Markovnikoff rule in the Wacker reaction and in the oxymercuration of propylene.

Mössbauer-Effekt von 57Fe und 119Sn in Palladiumlegierungen verschiedenen Wasserstoff-Gehaltes

AbstractThe isomer shifts of 57Fe and 119Sn in Pd/Fe and Pd/Sn alloys of different compositions have been studied as functions of hydrogen content. In both systems the isomer shifts start to increase steeply at hydrogen contents which bring up the electron concentration in the alloy to 0.55 additional electrons per metal atom (compared to pure Pd). In accordance with results from other experimental methods each Fe atom has been found to donate 3 and each Sn atom 3.5 electrons to the bands of the alloy. The increase of the isomer shift is shown to follow the rise of the Fermi level when the bands are filled up gradually. It can be correlated to Friedel's model of virtual bound states. The results obtained confirm the connections developed earlier between the absorption of hydro-gen and the electronic structure of Pd and its alloys. They agree with conclusions drawn from magnetic behaviour and from electronic specific heats at low temperatures. They do not verify, how-ever, a direct relation to the lattice constants in these systems. It is not yet obvious how to correlate our results with the value of 0.36 d-holes in pure Pd obtained recently from measurements of the de Haas-van Alphen effect; possible deviations from the rigid-band model are discussed.