SCF Xα SW Research Articles

X-Ray Spectroscopic Study of the PdxC60Chemical Bonding

AbstractThe CKα -emission spectra of the PdxC60 compounds were obtained. To interpret the spectrum and study the Pd - C60 chemical bond structure, the SCF Xα-SW calculations of the clusters simulating the bonding between two fullerene molecules and a Pd bridge atom were carried out. On the base of the obtained data, a diagram of the electron interaction between the Pd atoms and fullerenes was constructed.

Oxygen vacancy in perovskite oxides: Electron structure calculation by the SCF Xα, SW technique

Abstract The electron structure of the oxygen vacancy in SrTiO3 has been computed for the first time in frames of the approach that does not use a basis. The SCF Xα SW technique is used for this purpose. The clusters considered have 4 coordination spheres included. A satisfactory agreement with experiment is obtained for the cluster modeling the ideal crystal. It is found that the lowest unoccupied state of the cluster modeling the double-charged oxygen vacancy V++ o is of the alg symmetry, and it is localized in the sphere of vacant site for 34%, in cation spheres -for 20%. The potential reaches its maximum value in the vicinity of vacancy center. It means that a strong localization of an alg-state in the vicinity of V++ o is possible only due to the multiple scattering of the electron wave at the nearest neighbors. Perovskite, oxygen vacancy, electronic structure.

1S core‐level shifts of Al and Ar atoms in aluminum clusters

AbstractTheoretical 1s core‐electron binding energies are presented for Al and Ar atoms in free space and in AlAl12, AlAl12Al6, and ArAl12 clusters. The binding energies have been calculated by the self‐consistent field Xα scattered‐wave (SCF Xα SW) method using various exchange parameters and different atomic‐sphere overlaps. The atom/cluster binding‐energy shifts have been obtained both from the Slater's transition‐state energies and from the total‐energy differences; these values are in better agreement with each other if calculated with proper overlapping than if with nonoverlapping spheres. A comparison with available experimental and theoretical data is given as well.

Peculiarities of A1NbO3compounds energy band structure

Abstract Peculiarities of the energy band structure of the A1NbO3 type compounds have been revealed by from a comparison between the results of an X-ray spectroscopic study and the data of an SCF Xα-SW calculation of the cluster Nb6O6+ 12. Substantial hybridization of the Nb d- and O p-states indicates the substantial covalence of Nb-O chemical bond. In AgNbO3, in contrast to NaNbO3 and KNbO3, a contribution of the silver states to the valence and conduction bands-was observed, that results in certain changes of the energy band structure.

An SCF Xα SW calculation of Pt X-ray absorption spectra in chloride complexes: Pre-edge structure, XANES and EXAFS

The results of an SCF Xα SW calculation of Pt L 1 and L 2,3 X-ray absorption spectra in the complexes PtCl 4 2− and PtCl 6 2− at photoelectron energies from −20 to + 210 eV have revealed the main details of the pre-edge structure and the origins of XANES and EXAFS.

Xanes of the Pd and Pt atoms in square and octahedral chloride complexes

The fine structure near the ionization threshold in metal X-ray L-absorption spectra of the clusters PdCl 2− 4, PtCl 2− 4, PdCl 2− 6 and PtCl 2− 6 simulating solid complex compounds of the type K 2PdCl 4 and so on has been calculated using the SCF Xα SW method. Pt L 3 absorption spectra for the complexes K 2PtCl 4 and K 2PtCl 6 have been obtained using synchrotron radiation. The pre-edge white line and the near-edge fine structure (XANES) in Pd and Pt spectra of these square and octahedral chloride complexes have been shown to arise, respectively, from electron excitation to a vacant bound molecular orbital (e g for octahedral and b 1g for square complexes) and from photoelectron resonance elastic scattering by the metal atom and its first coordination sphere. The calculations indicated no intense pre-edge transitions for the metal L 1 spectra of these complexes and the XANES was shown to be due to several intense narrow shape resonances of the t 1u and a 2u, e u for octahedral and square complexes, respectively.

An SCF X?SW study of the electronic structure and X-ray and photoelectron spectra of Fe(II) and Fe(III) hexacyano complexes in a cluster approach

The electronic structure of the hexacyano complexes [Fe(CN)6]4− and [Fe(CN)6]3− as clusters of the cyanide complex salts has been calculated by the SCF XαSW method. Theoretical photoelectron, X-ray emission and absorption spectra have been constructed. The contribution of the resonance emission to the X-ray emission spectra has been estimated. On the basis of detailed comparison of the theoretical and experimental spectra an assignment of the fine structure of the spectra has been proposed.

Calculation of lower electronic states of the GaO and InO molecules by the SCF-X? scattered wave method

In the overlapping atomic spheres approximation of the SCF-Xα SW method in different variants (spin-restricted, spin-unrestricted, and quasirelativistic), we have calculated fragments of the potential curves for the electronic ground state (X 2∑) and the lower excited states (1 2π, 2 2∑, 2 2π, 3 2∑) of the GaO and InO molecules. We have calculated the spectroscopic constants (Te, ωe, ωexe, Be, αe, Re, Ae) for the molecules in the indicated states, the matrix elements for electronic transitions from the electronic ground state to the excited states, the Franck-Condon factors for the transitions 3 2∑, 2 2π, 2 2∑ ↔ 1 2π, X 2∑ (v′, v″ ≦10). For the InO molecule, we discuss the effect of relativistic corrections on the calculated molecular constants.

SCF-Xα scattered wave cluster study of molecularly adsorbed NO on Ni

SCF-Xα SW calculations have been performed on model clusters representing molecularly adsorbed NO on different sites of Ni surfaces: on-top and fourfold hollow positions on Ni(100) and a threefold site on Ni(111). The chemisorption bond is found to be formed through adsorbate-to-metal donation mainly via 4σ̃gs and 1π̃gp orbitals and back donation into the 2π ∗ orbital of NO. The molecular 2π ∗ orbital interacts with a manifold of substrate levels leading to a “broadening” of this level. A strong mixing of the 2π ∗ orbital both to the 1 \\ ̃ gp cluster orbital and to the band like 2π manifold leads to a weakening of the intramolecular bond of the adsorbate, especially for hollow site adsorption. The chemisorptive bond strength is found to increase with the metal coordination of the adsorption site leading to a definite preference of hollow positions over on-top positions.

Mössbauer studies of FeSn molecules isolated in rare-gas solids and SCF–Xα–scattered-wave molecular-orbital analyses of Sn2and FeSn diatomic molecules

Iron–tin molecules were isolated in rare-gas solids and studied using both 57Fe and 119Sn Mössbauer isotopes. Experiments at very dilute concentrations were performed to detect FeSn diatomic molecules. Larger clusters were identified by concentration dependence studies and Monte Carlo calculations. The 57Fe and 119Sn isomer shifts (IS) for FeSn diatomic molecules suggest a covalent bonding between Fe and Sn atoms. Similar behaviour was observed for large iron–tin clusters (FexSny; x, y 3). SCF–Xα–SW calculations were performed for Sn2 and FeSn diatomic molecules. Sn2 shows a 3∑g ground state and gives a quadrupole splitting (QS) consistent with the experimentally measured value at an equilibrium distance of 2.75 Å. The most probable ground state for FeSn is a 7Δ{σ2(3dFe, 5sSn)σ1(3dFe)σ2(4sFe 5pSn)σ2(4pFe,5pSn)π2.75(3dFe)δ2.25(3dFe)π1(5pSn)} configuration which gives the QS values for iron and tin atoms in agreement with the experimentally measured values at an equilibrium distance of 2.5 Å.

On the origin of satellite peaks in valence photoemission from CO ON Cu(110)

The valence-level photoelectron spectrum of CO absorbed on copper surfaces exhibits extra features in the region 10–20 eV below E F which are attributed to multielectron excitations. We have recorded the satellite intensity as a function of photon energy in the system CO/Cu(110) using synchrotron radiation. It is found that the occurrence of all satellites, including some which are observed for the first time, can be explained in terms of the SCF Xα SW model calculations by Messmer et al.

Calculation of photoelectron spectra of chloromethanes

Photoelectron spectra of chloromethanes have been calculated by the SCF Xα SW method. Results of the present work are in significantly better quantitative agreement with experiment data than are the results of other theoretical methods.

Bulk properties or not: The electronic structure of small metal clusters

The dependence of the properties of small copper clusters on their size, and their relationships to the properties of the bulk metal have been studied through ab initio SCF calculations (with the emphasis on the clusters Cu8 and Cu13). The basis set used is of double-zeta quality for the valence shells 3d and 4s. The analysis focuses on the following properties of the clusters: geometrical structure, binding energy, and distribution of energy levels. For the 13-atom cluster, the icosahedron is found more stable than the cubo-octahedron corresponding to the fcc structure of the bulk metal. The binding energy per atom increases almost linearly with the number of atoms of the cluster. From the orbital energy values, the sets of 3d and 4s levels are well separated for Cu8 and just begin to overlap for Cu13. This situation looks rather different from the one for the bulk metal where the s band totally overlaps the d band. The relationship between the orbital energies from the ab initio SCF calculations and the ionization potentials is discussed. For the 13-atom cluster, the relaxation effect is probably small enough that the above conclusions, based on Koopmans’ theorem and the use of orbital energies, should not be altered by including it. On the whole, the ab initio results contradict the conclusion of the SCF–Xα–SW calculations that the electronic structure of small metal clusters and of the bulk metal are not fundamentally different and that not many atoms are needed in a cluster to have a resemblance to the bulk. This idea was based on the analysis of the orbital energy values from the Xα calculations, which showed that the ’’d band’’ was completely overlapped by the ’’s band.’’ However, this represents probably a spurious effect, since the Xα eigenvalue differs from the corresponding ionization potential by a ’’self-interaction term,’’ with rather different values for the orbitals of the 3d type and of the 4s type.

A SCF Xα SW study of the shake-up in TiCl 4

The Ti 2p electron shake-up spectrum in TiCl 4 is calculated using SCF Xα SW method. Results showed that the low-energy satellite can be ascribed to ligand → metal charge-transfer transitions. However, the nature of the intense peak at 9.8 eV cannot be explained within the one-electron model. An anomaly is noted in the eiperimental spectra of the titanium halides.

Calculation of multiplet structures in shakeup spectra by the Xα method

The energy expression for calculating upper and lower states of shakeup lines in core line photoelectron spectra were derived. Using the SCF–Xα–SW approximation, we have obtained satisfactory results in molecules with strong hole–valence coupling. The results also suggested configuration interaction is important for molecules with low lying excited states.

Charge distributions and chemical effects: Part XV. SCF—Xα—SW studies of alkanes

SCF—xα—SW calculations have been performed for the electronic structure of methane, ethane, propane, isobutane and neopentane. The touching and overlapping sphere models with different degrees of overlap were used. The charge distributions were partitioned into atomic charges by means of a modified overlapping sphere model. These charges which indicate a C +H − polarity reflect closely the customary inductive effects and are unique in that they represent the only set of theoretically determined charges which can be related directly to experiment.

Dependence of stability, bond strength and electronic structure of dimetal units upon atomic number, oxidation number and chemical environment

The electronic structures of the Cr2 and Mo2 units in the form of neutral diatomic molecules, charged diatomic molecules and coordinated by ligands have been investigated by SCF–Xα–SW calculations, supplemented by projection of the Xα MOs in atomic orbital basis sets (the PXα procedure). The results are compared with the experimental data on Cr2, Mo2 and the many CrII2Ln and MoII2Ln complexes.

SCF Xα SW calculations of chemical shifts of X-ray and electron emission lines and relaxation properties of SiX 4 molecules

SCF Xα SW calculations of the 1s and 2p binding energies, KLL Auger energies and Kα transition energies for the molecules SiH 4, SiCl 4 and SiF 4 and the corresponding atomic Xα calculations for charged free silicon ions have been carried out. The results provide information about relaxation properties and anomalous chemical Kα shifts in hydrides.

Analysis of the CsNpF6 optical spectrum

A new analysis is given of the CsNpF6 optical spectrum, which removes several features of a previous analysis which were questionable. Possible vibronic structure, SCF–Xα–SW calculations, and analyses of related compounds have been used as a basis for the present investigation. It was found that configuration interaction effects are significant and cannot be neglected. By inclusion of linear CI terms, a fit to 33 assigned levels gave an rms deviation of 140.6 cm−1 in a least-squares refinement. The parameters determined are F2=202.2, F4=14.26, F6=1.517, ζ=2137, A4〈r4〉=1431, A6〈r6〉=112.6, α=195.2, β=−5798, and γ=9582 cm−1.

A comparison of the electronic structure of some Group 6A dimetal tetracarboxylates using photoelectron spectroscopy

He(I) and He(II) photoelectron spectra are presented for [Cr2(O2CR)4](R = Me or Et), [CrMo(O2CMe)4], and [Mo2(O2CR)4](R = H, Me, CMe3, or CF3). Ionization energies and intensities are discussed in relation to ab initio and SCF–Xα-SW calculations. A σ2π4δ2 configuration for the metal electrons gives the most plausible explanation for all spectra, but the 2Σ, 2Π and 2Δ ion states lie much closer in energy for the dichromium tetracarboxylates than for the molybdenum analogues.