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The electronic structure of Croconic Acid in the condensed phase has been studied by comparing core level and valence band x-ray photoelectron spectroscopy experiments and first principles density functional theory calculations using the Heyd-Scuseria-Ernzerhof screened hybrid functional and the GW approximation. By exploring the photoemission spectra for different deposition thicknesses, we show how the formation of the hydrogen bond network modifies the O 1s core level lineshape. Moreover, the valence band can be explained only if the intermolecular interactions are taken into account in the theoretical approach. [ABSTRACT FROM AUTHOR]

The adsorption of NO2 molecules on defective multiwalled carbon nanotubes has been studied by soft-x-ray photoemission. The valence band and carbon core-level spectra have been acquired before, during, and after NO2 exposure. The spectra show a reversible decrease of the density of states at the top of the valence band when NO2 molecules are adsorbed on the (carbon nanotubes) CNTs. No shift of the C 1s spectra has been observed. Theoretical calculations, using density-functional theory, have been performed on the CNT+NO2 system, considering semiconducting nanotubes with different diameters and introducing a Stone–Wales [Chem. Phys. Lett. 128, 501 (1986)] defect. The calculation confirms the decrease of the density of states at the top of the valence band in the CNT+NO2 system, while close to the adsorption site new states appear very close to the Fermi level. [ABSTRACT FROM AUTHOR]

First-principles calculations within the density functional theory have been performed in order to investigate ozone adsorption on carbon nanotubes. Particular emphasis is placed on the effects of Stone–Wales-like defects on the structural and electronic properties of (i) ideal tubes and (ii) tubes in the presence of ozone. Our results show that structural deformations induced on the pure carbon nanotubes by Stone–Wales defects are similar, as expected, to those induced on graphite; for the (10,0) tube, the semiconducting character is kept, though with a small reduction of the band gap. As for the ozone adsorption, the process on ideal nanotubes is most likely physisorption, though slightly stronger if compared to other previously studied molecules and consistent with the strong oxydizing nature of O3. However, when ozone adsorbs on Stone–Wales defects, a strong chemisorption occurs, leading to relevant structural relaxations and to the formation of a CO covalent bond; this is consistent with experimental observations of CO functional groups, as well as of the liberation of CO gas phase and of the formation of C vacancies, thus explaining the consumption of the nanotube film upon ozone exposure. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The electronic structures (especially 4f states) of hexagonal and tetragonal erbium silicides are investigated within density functional theory. Contrary to previous theoretical studies on these compounds, Er 4f electrons are treated as valence state electrons, explicitly taking into account the on-site Coulomb interactions. Total energy calculations show that the relaxed hexagonal ErSi1.7 is more stable than the tetragonal structure, consistently with related experimental observations. The calculated total density of states of the hexagonal ErSi1.7 agrees well with the experimental valence-band spectrum in a wide energy range from 0 to 12 eV below the Fermi level. In addition, our study indicates that the occupied 4f states in erbium silicides can also locate in the energy range of 0–4.0 eV below the Fermi energy, much different from the prediction of the previously adopted Er ion model. [ABSTRACT FROM AUTHOR]

By means of ab initio calculations, we present a theoretical study of Pd porphyrin deposited on an Al(1 1 1) metallic substrate, focusing on the interaction between molecules and metal surfaces and on the alignment of molecular levels at the interface. The changes induced on the relevant electronic properties by the use of a different parametrization (i.e. local density approximation vs generalized gradient approximation) of the exchange-and-correlation potential within the density functional theory are discussed. The results show that the molecule–substrate interaction is rather weak and that the character of the contact is rectifying. [Copyright &y& Elsevier]

The electronic structure of croconic acid in the gas phase has been investigated by means of core level and valence band photoemission spectroscopy and compared with hybrid Heyd-Scuseria-Ernzerhof density functional theory calculations. The results have been compared with the corresponding ones of the condensed phase. In the gas phase, due to the absence of hydrogen bond intermolecular interactions, the O 1 s core level spectrum shows a shift of binding energy between the hydroxyl (O-H) and the carbonyl group (C=O) of 2.1 eV, which is larger than the condensed phase value of 1.6 eV. Interestingly, such a shift decreases exponentially with the increase of the O-H distance calculated from theory. The significant differences between the gas and condensed phase valence band spectra highlight the important role played by the hydrogen bonding in shaping the electronic structure of the condensed phase. [ABSTRACT FROM AUTHOR]

Abstract: The effect of the proximity of Au on the electronic and magnetic properties of La0.66Sr0.33MnO3 (LSMO) has been investigated by means of ab initio calculations within the density-functional theory. The calculations show an orbital reconstruction of the interfacial Mn, which is due more to the presence of a discontinuity rather than to a real chemical interaction with Au atoms. In fact, the same orbital reconstruction is found in the free LSMO surface. In both cases of Au/LSMO and LSMO surface, the Mn magnetic moments change very little with respect to the bulk case. In general, the calculations show a negligible influence of the Au atomic layer on LSMO at an ideal interface, with the LSMO surface magnetic and electronic properties essentially unchanged. [Copyright &y& Elsevier]

The electronic properties of tris(8-hydroxyquinolinato)aluminium(III) (AlQ3) have been revisited using the screened hybrid Heyd-Scuseria-Ernzerhof density functional theory. We show that such approach very well accounts for the experimental occupied (valence band spectrum) and unoccupied (inverse photoemission spectrum) states. Furthermore, the density of states projected onto nitrogen, oxygen, and carbon are compared with soft x-ray adsorption and emission spectroscopy, showing a very good agreement between theory and experiments. Finally, a fully theoretical interpretation of the carbon 1s core level is proposed. [ABSTRACT FROM AUTHOR]