Electronic structure of palladium in the presence of many-body effects (original) (raw)
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Lattice dynamics of palladium in the presence of electronic correlations
Physical Review B
We compute the phonon dispersion, density of states, and the Grüneisen parameters of bulk palladium in the combined density functional theory (DFT) and dynamical mean-field theory (DMFT). We find good agreement with experimental results for ground state properties (equilibrium lattice parameter and bulk modulus) and the experimentally measured phonon spectra. We demonstrate that at temperatures T 20 K the phonon frequency in the vicinity of the Kohn anomaly, ωT 1(qK), strongly decreases. This is in contrast to DFT where this frequency remains essentially constant in the whole temperature range. Apparently correlation effects reduce the restoring force of the ionic displacements at low temperatures, leading to a mode softening.
Physical review, 1986
Palladium metal clusters with an average diameter of 14 A embedded in a carbon matrix have been studied by synchrotron-radiation x-ray absorption measurements. The data analysis of the L2,3 edge (p-d transitions) shows (a) a strong reduction of the absolute value of the absorption compared to the bulk, (b) a shift towards higher binding energies of about 2 eV, and (c} a broadening of the same structures. We explain these effects as mainly due to a change of the d density of states at the Fermi level, since the L~edge (s-p transitions) does not show similar effects. The extended x-ray absorption fine-structure analysis reveals an important increase of about 3% of the first-nearest-neighbor distance, in contrast with other metals which show a lattice contraction.
Density-Functional andab initio computational studies of palladium clusters
International Journal of Quantum Chemistry, 1993
Nonlocal density-functional and correlated ab initio methods have been used to compute singlettriplet separations for the Pd atom and Pd2, as well as the dissociation energies of the latter in its ground and first excited states. The results are in good agreement with the available experimental data and with other high-level calculations. Single-point local density-functional computations were carried out for Pd clusters up to PdZ2 (1012 electrons). The interaction energy per Pd-Pd bond appears to be approaching a limiting value for Pd22.
Quantum chemical study of small palladium clusters
Surface Science, 1998
The extended Hü ckel method with an electrostatic two-body correction has been used to find the structure of small Pd n clusters for n=2-13. Twins formation, with metal-metal bond lengths slightly smaller than those of bulk palladium, was found to be the preferential direction for cluster growth in the absence of external field. In accordance with the experimental results, these closepacked particles show a significant split in the valence d-zone. The energetic gap between HOMO and LUMO narrows from 3.217 to 0.68 eV as the cluster grows from two to 13 atoms. The LUMO has a bonding character toward Pd-Pd bonds, whereas HOMO is antibonding, so one can suggest that both donating and accepting interactions are favorable for strengthening of clusters. Occupation of 5s and 5p orbitals increases during cluster growth, while the net charge on the outer atoms remains very small. The results obtained for two to six atomic clusters are in good agreement with first principle calculations. Very close similarity with Rh cluster growth was observed.
Physical Review B, 1987
We have performed calculations of the electronic states of palladiumnoble-metal disordered alloys using an improved version of the tight-binding coherent-potential-approximation (TB-CPA) formalism. Our results for Pd-Ag are in excellent agreement with both experiment and the Korringa-Kohn-Rostoker (KKR) CPA. For Pd-Au we also obtain good agreement with specific-heat measurements. For Pd-Cu, probably due to charge-transfer effects, we do not obtain satisfactory agreement with experiment at the Cu-rich end. Our calculations indicate that if (a) highly accurate Slater-Koster parameters are used and (b) all the orbitals are included in the CPA conditions (i.e. , not using a one-level TB model), the TB-CPA gives results that are equivalent to those of the KRR-CPA except in cases where off-diagonal disorder might be important.
On electronic structure of H2 in palladium
Czechoslovak Journal of Physics, 1992
Using quasi-relativistic CNDO method the electronic structure of 1[Pd14... nH] q clusters (n = 0 or 2) with various total charges, q, is investigated for various H-H configurations. All systems are more stable for q = -2 than for q = 0. Lower unit cell dimensions cause the energy stabilization of the tt-H subsystem, the dihydrogen charge is more positive and the H-H bond is stronger. The results on electronic structure calculations indicate the existence of higher electron states with significant shifts of energy minima.
Journal of Cluster Science, 2014
Based on density functional calculations on model systems, the electronic structure of medium and large ligated palladium clusters is discussed herein. Among all the studied clusters, the electronic structure of Pd 30 ðCOÞ 26 ðPR 3 Þ 10 , Pd 69 ðCOÞ 36 ðPR 3 Þ 18 and Pd 145 ðCOÞ 56 ðPR 3 Þ 30 clusters is analyzed in details. It is shown that the evolution of the band gap can be correlated to the average Pd-Pd bond length rather than n, the nuclearity of the cluster.
Quantum chemical study of neutral and single charged palladium clusters
Journal of Molecular Catalysis A: Chemical, 2000
The extended Huckel EH method with an electrostatic two-body correction, has been used in order to determine thë structures of small single charged Pd clusters with n s 2-13 and to compare them with the neutral ones. The results for n Ž . Pd and Pd are compared with density functional DFT calculations. Both cation and anion formations were found to 2 3 strengthen the clusters due to the bonding character of their HOMO and antibonding nature of LUMO. The twin formation with bond lengths significantly smaller than those in the bulk palladium and in the corresponding neutral particles was found to be the preferential way of growth for anionic clusters; cationic clusters show a more complicated behavior. The promotion of occupation of Pd 5s AOs is suggested to be responsible for the formation of 3D structures, whereas the stability of the planar configurations is attributed to the appearance of the vacancy in the valence 4 d-shell. As a result of stronger intermetallic interaction in charged clusters, both excess and deficit of electron density were found to cause the significant broadness of the d-zone. q
Size-dependent lattice structure of palladium studied by x-ray absorption spectroscopy
Physical Review B, 2007
X-ray absorption spectroscopy measurements have been made on 7-, 12-, and 23-nm palladium particles, along with bulk material as reference. With decreasing particle size, the extended x-ray absorption fine spectra reveal a substantial contraction of the nearest-neighbor distance and a reduction of the average coordination number, but an increasing Debye-Waller factor. Meanwhile, the x-ray absorption near edge spectra show a decreasing density of unoccupied states with decreasing particle size.