Xα SW Method Research Articles

Quantum-chemical investigation of the nature of interatomic bonding in molybdenum and uranium clusters

Calculation of the electronic structure of regular and distorted octahedral clusters of uranium and molybdenum has been carried out by the relativistic Dirac-Slater Xα-SW method. The cluster model can describe the b.b.c. γ-uranium structure stabilization by molybdenum. The important role of the inner uranium 6p-AO in the interatomic bonding is pointed out.

On the calculation of exchange coupling constants in transition metal dimers by the Xα-SW method

The main theoretical models for the calculation of the singlet triplet separation in dinuclear systems containing transition metal ions are briefly reviewed and some examples of applications are reported. The Xα-SW model is applied to calculate the magnetic structure of [(OH)4 Cu (μ -0)Cu (OH)4]6- and of the heterodinuclear ferromagnetic dimer [(NH3 )2 Cu (μ-OH)2 VO (OH)2 ]. A nice agreement with the experimental results has been obtained.

Electronic structure and the x-ray and photoelectron spectra of hexacyano-complexes of Fe(II) and Fe(III) in the cluster approximation by the SCF-X?-SW method

The present study of cyano complexes leads to the following conclusions. 1. The x-ray and PE spectra are directly related to the results of quantum-chemical calculations: the IP and the partial charges or populations. Thus the complete set of theoretical x-ray and PE spectra apparently represents one of the most successful ways of obtaining a clear graphical representation of the results of quantum-chemical calculations. 2. The complete set of x-ray and PE spectra provide a good test for verifying quantum-chemical theory, for selecting a model of the electronic structure, and for refining the procedure for carrying out the calculations, in the present case of the Xα-SW method the method for selecting the radii of the atomic spheres. 3. With the optimum selection of the radii of the atomic spheres, the Xα-SW method describes with satisfactory accuracy those aspects of the electronic structure of coordination compounds that are reflected in the x-ray (except the XE Kβ5 spectra) and PE spectra of the valence orbitals.

Electronic structure and photoelectron spectra of osmium and ruthenium tetraoxides

The Xα-SW method has been used in the nonrelativistic and quasirelativistic approximations to calculate the electronic structures of OsO4, RuO4, and FeO4. When the 5d element is replaced by a 4d or 3d one, the electron-density redistribution is due mainly to the d electrons. All the d electrons in FeO4 are localized on the iron atom, which markedly reduces the ionic and covalent bonding on the transition from RuO4, to FeO4, which explains the instability of FeO4. The calculated spin-orbit splittings agree well with the structure of the PES bands, which enables one to establish the sequence of MO ionization energies unambiguously.

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.

ChemInform Abstract: COMPARATIVE STUDIES ON THE ELECTRONIC STRUCTURES OF TETRAFORMATODITUNGSTEN AND DIMETHYLTETRAFORMATODITUNGSTEN BY THE RELATIVISTIC Xα‐SW METHOD: A D3‐D3 METAL DIMER WITH A QUADRUPLE METAL‐METAL BOND

Chemischer InformationsdienstVolume 16, Issue 45 Organoelement Compounds ChemInform Abstract: COMPARATIVE STUDIES ON THE ELECTRONIC STRUCTURES OF TETRAFORMATODITUNGSTEN AND DIMETHYLTETRAFORMATODITUNGSTEN BY THE RELATIVISTIC Xα-SW METHOD: A D3-D3 METAL DIMER WITH A QUADRUPLE METAL-METAL BOND M. D. BRAYDICH, M. D. BRAYDICHSearch for more papers by this authorB. E. BURSTEN, B. E. BURSTENSearch for more papers by this authorM. H. CHISHOLM, M. H. CHISHOLMSearch for more papers by this authorD. L. CLARK, D. L. CLARKSearch for more papers by this author M. D. BRAYDICH, M. D. BRAYDICHSearch for more papers by this authorB. E. BURSTEN, B. E. BURSTENSearch for more papers by this authorM. H. CHISHOLM, M. H. CHISHOLMSearch for more papers by this authorD. L. CLARK, D. L. CLARKSearch for more papers by this author First published: November 12, 1985 https://doi.org/10.1002/chin.198545257AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume16, Issue45November 12, 1985 RelatedInformation

High-resolution HeI and HeII photoelectron spectra of the Zn 3d and Cd 4d orbitals in the zinc and cadmium dihalides: Ligand field splittings and intensity variations

We have recorded the high-resolution HeI and HeII photoelectron spectra of the Zn 3d and Cd 4d levels in gas-phase MX 2 molecules (M = Zn, Cd; X = Cl, Br, I). The d level spectra split into five peaks due to the combined effect of spin-orbit splitting and ligand field splitting on the d 9 hole state, and the spectra have been fitted to a crystal field hamiltonian involving the cubic ( C 4 0) and non-cubic ( C 2 0) parts of the field from the halide ligands. Additional peaks in some spectra are due to vibrational splitting and configuration interaction. The ¦ C 2 0¦ value increases substantially from the chloride to the iodide for both Zn and Cd. Calculations of both the crystal field ( C 2 CF 0) and valence ( C 2 val 0) parts of C 2 0 show that the increase in observed C 2 0 is due to the C 2 val 0 term attributed to the increase in covalency from the chlorides to the iodides. Shifts in the peak position due to the 2Σ 1 2 g and 1Π 3 2 g states from those expected on the ligand field basis. are attributed to slight bonding effects. These effecs cause a large discrepancy between calculated and observed C 4 0 values. The intensities of the five Zn 3d peaks change markedly from HeI- to HeII-excited spectra. The Xα SW method has been used to calculate the intensities of the σ, π and δ 3d orbitals as a function of photon energy. These calculations show dramatic changes in intensity due. for example. to shape resonances. There is usually qualitative agreement between calculated and observed intensities.

Effect of chemical structure on the electron density at the tellurium nucleus

This paper reports results of a study in which the Xα-SW method is employed to deduce estimates of the differences in the electron densities at the Te nucleus in some compounds. On the basis of these estimates some assertions are deduced to the calibration problem of the Mossbauer nuclide125Te and to the chemical influence on the IC of the 35.5 keV M1+E2 transition in125Te.

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.

Estimates of the electron charge densities at the iodine nucleus in some compounds

This paper reports results of a study in which the Xα-SW method is employed to deduce estimates of the differences in the electron-charge densities at the I nucleus in some compounds. On the basis of these estimates some assertions are deduced to the calibration problem of the Mössbauer nuclide 129I and to the halflife variations in the EC ( 123I and 125I) and IC ( 129I) decay. A comparison is made with the experimental data avai

Ionization energies of the N2, CO, CO2, N2O, C2H2 and SiH4 molecules calculated by universal model potential

A modified XαSW method with universal potential (MXαSWU) was used to calculate ionization energies of the N2, CO, CO2, N2O, C2H2 and SiH4 molecules. The calculated energies are in agreement with experiment and other calculations.

The electronic structure and chemical bonding in rare earth chalcogenides according to the XαSW method—II : NdS, EuS and ErS

Electronic structure calculations for (NdS 6) 10− (EuS 6) 10−, (ErS 6) 10− clusters in NdS, EuS and ErS have been performed with the Xα SW method. The results agree well with the photoemission spectra. Analyses of charge distributions reveal that in spite of the localized nature of the 4 f-derived MO's, the 3 p S-states contain admixtures of both 4 f- and 5 d-states, most noticeably for NdS. The decrease of covalency in the direction NdS→EuS→ErS corresponds to the changes of melting temperatures, and dissociation energies for the crystal and gaseous RE monosulfides.

The electronic structure and chemical bonding in rare earth chalcogenides according to the Xα SW method—I : EuO, EuS and EuSe

Calculations of the electronic structure for (EuO 6) 10− (EuS 6) 10−, and (EuSe 6) 10− clusters, which represent the nearest-neighbour sphere surrounding Eu in EuO, EuS, EuSe, have been made by the Xα SW method. The contour maps for valence MO's have been drawn. The MO energy diagrams are in reasonable agreement with experimentally derived band structures. In spite of the localized nature of 4 f-derived states, there are noticeable admixtures of 4 f-states to the valence band. The 5d Eu states hydridize with the chalcogenide valence states, and the covalency of the chemical bonding decreases from EuO to EuSe, which can explain the decrease of elastic modulus, microhardness and chemical stability.

The electronic structure and chemical bonding in rare earth chalcogenides according to the Xα SW method. II. NdS, EuS, ErS

The electronic structure and chemical bonding in rare earth chalcogenides according to the Xα SW method. II. NdS, EuS, ErS

The electronic structure and chemical bonding in rare earth chalcogenides according to the Xα SW method. I. EuO, EuS, EuSe

The electronic structure and chemical bonding in rare earth chalcogenides according to the Xα SW method. I. EuO, EuS, EuSe

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 single orbital relaxations accompanying core ionization in the isoelectronic ten electrons hydrides by the Xα–SW method

SCF-Xα-SW calculations are performed on the ground state and core 1s hole state for CH4, NH3, H2O and HF using the overlapping sphere model, Table 1 contains the molecular charge reorganization after the renormal of an 1s electron in these molecules. The screeming of the core is further discussed. (AIP)

Use of XαSW calculations for parametrising the CNDO method for the heavier elements. II. Tests for the elements aluminium to sulphur

In Part I (Mol. Phys. 35, 1681 (1978)) we used results from the Xα scattered wave (XαSW) method for guiding the parametrisation of the complete neglect of differential overlap (CNDO) method for clusters of silver, and we proposed the extension of this approach to other heavier elements for which CNDO schemes are not well developed. The main purpose of the present paper is to test this approach for the elements aluminium to sulphur for which more information is available. XαSW calculations have been made for the molecular clusters Al7, Si5H12, and P4, and comparisons made with experiment and with other calculations where possible. The charge distributions and transition-state energies, along with information obtained previously for S8 by Salahub et al., have been used to derive new parameters (designated CNDO/HM) for the elements aluminium to sulphur essentially following the procedure in Part I. Calculations using these parameters have then been tested against an XαSW calculation made here for an Al10 cluster (which simulates the (111) surface of aluminium), and against other calculations made previously for P8, P4S3, SiH4, PH3, H2S, and SO2. Comparisons are also made with results from the CNDO/2 scheme. Generally the CNDO/HM procedure seems at least as successful as CNDO/2.

Valence and Rydberg excited states of H2S: An SCF-Xα-SW molecular orbital study

SCF-Xα-SW calculations have been performed for H2S in the ground state, in ionic states resulting from the vertical removal of a valence electron, and in 36 singlet and triplet excited states resulting from the vertical excitation of an electron from the 2b1 or the 5a1 molecular orbitals to various virtual orbitals. Excellent agreement for the transition energies is found both with the experimental ultraviolet and photoelectron spectra and with recent large-scale configuration interaction calculations. The average absolute difference between the Xα-SW and CI results for the 26 cases where both exist is only 0.24 eV. The intrinsic advantages of the Xα-SW method over the traditional LCAO or one-center approaches for the treatment of Rydberg states are delineated. Contour plots of the excited orbitals have been generated and these are used to illustrate some of the conceptual problems related to the Rydberg-valence distinction. Finally, a brief speculative discussion of the possible photochemical implications of the character of the two excited orbitals involved in the first absorption band is given.