Search results for "ELECTRONIC STRUCTURE"
showing 10 items of 722 documents
Theoretical study on the effect of backbone conformation on the electronic structure of poly(di-n-butylsilane)
1993
Abstract We present the results of valence effective Hamiltonian (VEH) calculations on the electronic structure of poly(di-n-butylsilane) in its all-trans and 7/3 conformations. The band structure of all-trans conformation is analyzed in detail and the effects of the backbone conformation on the electronic and optical properties are studied. The VEH results for the 2/1 and 7/3 conformations are in excellent quantitative agreement with photoemission and UV-absorption data and show the reliability of the VEH method to deal with organopolysilanes.
Theoretical calculations on the valence electronic structure of naphthalocyanine: comparison with experimental photoemission data
1993
Abstract We present a theoretical investigation of the electronic structure of metal-free 2,3-naphthalocyanine (2,3-H2Nc) using the valence effective Hamiltonian (VEH) technique. The VEH-DOVS curves obtained for 2,3-H2Nc are correlated with those calculated for naphthalene molecule and a one-to-one correspondence is found. From the electronic structure standpoint, naphthalocyanine has to be viewed as formed by joining four naphthalene moieties to the central carbon-nitrogen ring. An excellent quantitative agreement is found between VEH-DOVS curves and experimental photoemission data.
Theoretical study of the electronic spectra ofcis-1,3,5-hexatriene andcis-1,3-butadiene
1994
The electronic spectra forcis-1,3-butadiene andcis-1,3,5-hexatriene have been studied using multiconfiguration second-order perturbation theory (CASPT2) and extended ANO basis sets. The calculations comprise all singlet valence excited states below 8.0 eV, the first 3s, 3p, 3d Rydberg states, and the second 3s state. The four lowest triplet states were also studied. The resulting excitation energies forcis-hexatriene have been used in an assignment of the experimental spectrum, leading to a maximum deviation of 0.13 eV for the vertical transition energies. The calculations place the 11 B 2 state 0.04 eV below the 21 A 1 state. 16 excited states were studied incis-butadiene, using a CASPT2 o…
When Does Gold Behave as a Halogen? Predicted Uranium Tetraauride and Other MAu4 Tetrahedral Species, (M = Ti, Zr, Hf, Th)
2003
Quantum chemical calculations suggest that a series of molecules with the general formula MAu4 are stable, where M = U, Th, and a group-4 atom. They correspond to Au in the formal valence state -1 and indicate that gold can act as a ligand similar to the halogen series. Of the MAu4 species studied, UAu4, the first predicted mixed gold uranium compound, has a short M-Au bond distance, 2.71 A, which would locate Au between Br and I from the bond length point of view in the U-tetrahalide series. Energetically, the U-Au bond is weaker than the corresponding U-Br and U-I bonds.
Valence-band electronic structure of CdO, ZnO, and MgO from x-ray photoemission spectroscopy and quasi-particle-corrected density-functional theory c…
2009
The valence-band density of states of single-crystalline rock-salt CdO(001), wurtzite $c$-plane ZnO, and rock- salt MgO(001) are investigated by high-resolution x-ray photoemission spectroscopy. A classic two-peak structure is observed in the VB-DOS due to the anion $2p$-dominated valence bands. Good agreement is found between the experimental results and quasi-particle-corrected density-functional theory calculations. Occupied shallow semicore $d$ levels are observed in CdO and ZnO. While these exhibit similar spectral features to the calculations, they occur at slightly higher binding energies, determined as 8.8 eV and 7.3 eV below the valence band maximum in CdO and ZnO, respectively. Th…
Electronic structure of EuO spin filter tunnel contacts directly on silicon
2011
We present an electronic structure study of a magnetic oxide/ semiconductor model system, EuO on silicon, which is dedicated for efficient spin injection and spin detection in silicon-based spintronics devices. A combined electronic structure analysis of Eu core levels and valence bands using hard X-ray photoemission spectroscopy was performed to quantify the nearly ideal stoichiometry of EuO “spin filter” tunnel barriers directly on silicon, and the absence of silicon oxide at the EuO/Si interface. These results provide evidence for the successful integration of a magnetic oxide tunnel barrier with silicon, paving the way for the future integration of magnetic oxides into functional spintr…
Understanding the trend in the Curie temperatures ofCo2-based Heusler compounds:Ab initiocalculations
2007
The Curie temperatures for the Heusler compounds Co{sub 2}TiAl, Co{sub 2}VGa, Co{sub 2}VSn, Co{sub 2}CrGa, Co{sub 2}CrAl, Co{sub 2}MnAl, Co{sub 2}MnSn, Co{sub 2}MnSi, and Co{sub 2}FeSi are determined ab initio from the electronic structure obtained with the local-density functional approximation and/or the generalized gradient approximation. Frozen spin spirals are used to model the excited states needed to evaluate the spherical approximation for the Curie temperature. The spherical approximation is found to describe the experimental Curie temperatures very well which, for the compounds selected, extend over the range from 95 to 1100 K; as a function of the valence electron count, they sho…
Electronic structure of large disc-type donors and acceptors
2010
Searching for new pi-conjugated charge-transfer systems, the electronic structure of a new acceptor-donor pair derived from coronene (C(24)H(12)) was investigated by ultraviolet photoelectron spectroscopy (UPS). The acceptor coronene-hexaone (C(24)H(6)O(6), in the following abbreviated as COHON) and the donor hexamethoxycoronene (C(30)H(24)O(6), abbreviated as HMC) were adsorbed as pure and mixed phases on gold substrates. At low coverage, COHON adsorption leads to the appearance of a charge-transfer induced interface state 1.75 eV below the Fermi energy. At multilayer coverage the photoemission intensity of the interface state drops and the valence spectrum of neutral COHON appears. The sa…
Electronic structure of metal‐free phthalocyanine : A valence effective Hamiltonian theoretical study
1988
We present a valence effective Hamiltonian (VEH) nonempirical investigation of the electronic properties of metal‐free phthalocyanine. The valence one‐electron energy levels are related to those of the phthalocyanine components: benzene, pyrrole, and isoindole. From the electronic structure standpoint, phthalocyanine has to be viewed as formed by joining four benzene moieties to the central carbon–nitrogen ring rather than by combining four isoindole units through nitrogen bridges. Comparison of the VEH density‐of‐valence‐states curves with the experimental ultraviolet photoelectron spectroscopy (UPS) data is quantitatively excellent and allows for a complete interpretation of the experimen…
Theoretical characterization of the electronic properties of unsymmetrical phthalocyanine analogues
1993
Abstract The electronic structure of unsymmetrical phthalocyanine-based compounds is investigated using the nonempirical valence effective Hamiltonian (VEH) method. The VEH results predict a slight but continuous destabilization of the HOMO level and a monotonous narrowing of the HOMO-LUMO energy gap as the size of the system increases. The theoretical trends are found to agree with optical absorption experimental data and show that the optical properties of phthalocyanine can be monitored by adjusting the size of the π-conjugated macrocycle.