Search results for "functional"
showing 10 items of 4822 documents
Electronic and optical properties of CeO 2 from first principles calculations
2016
International audience; First-principles calculations of the electronic structure of CeO2 nanoparticles (NPs) were performed to investigate published experimental data obtained by different spectroscopies. The main features of the valence and conduction bands have been analyzed from the total and partial density of states. Several functionals were applied to interpret and quantify the optical properties, including the dielectric function, extinction coefficient and refractive index. It is found that the on-site hybrid functional B3PW91 modelled most suitably the band gap region of CeO2 NPs and consequently gave a more accurate band gap value. It also agreed very well with the experimental v…
Absolute acidity of clay edge sites from ab-initio simulations
2012
International audience; We provide a microscopic understanding of the solvation structure and reactivity of the edges of neutral clays. In particular we address the tendency to deprotonation of the different reactive groups on the (0 1 0) face of pyrophyllite. Such information cannot be inferred directly from titration experiments, which do not discriminate between different sites and whose interpretation resorts to macroscopic models. The determination of the corresponding pKa then usually relies on bond valence models, sometimes improved by incorporating some structural information from ab-initio simulations. Here we use density functional theory based molecular dynamics simulations, comb…
Diferrocenyl oligothiophene wires: Raman and quantum chemical study of valence-trapped cations
2011
A combination of Raman spectroscopy and density functional theory calculations is used to describe the structural and spectroscopic properties of the different isomeric cations of diferrocenyl quaterthiophenes. Isomerisation of the thienyl β-positions provides site selective oxidation, which gives rise to species that can interconvert by moving the charge over the bridge. The spectroscopic study allows us to describe a sequence of stationary trapped cationic, either ferrocenyl or thienyl, states which constitutes an energy cascade of accessible sites through which the charge transfer can proceed.
First-principles calculations of surfaceHcenters inBaF2
2010
H center, a hole trapped at an interstitial anion site, placed on the 111 surface of Barium fluoride BaF2 has been studied by using density functional theory DFT with hybrid exchange potentials, namely, DFT-B3PW. Two different configurations of surface H center are investigated carefully. Both surface H-center systems have strong relaxations because of the surface effect. In the configuration that the interstitial fluorine atom is within the surface, named case 1 in this paper, the unpaired electron is almost equally distributed onto the two atoms of the H center, which is quite different from the bulk H-center case. The other configuration with one of the F atoms of the H center located ab…
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 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…
Iso-valence Co(II) and mixed-valence Co(II/III) tetranuclear complexes: Synthesis, structure, magnetic properties and DFT study
2013
Abstract The reaction of Co(ClO4)2·6H2O with symmetrical N4O3 coordinating heptadentate ligand (H3L) in presence of triethylamine yielded cobalt(II) tetranuclear complexes [Co4(L)2](ClO4)2, 1. When the same reaction is carried out with sodium azide instead of triethylamine afforded tetranuclear mixed-valence Co(II/III) species, [Co4(L)2(μ1,3–N3)2](ClO4)2, 2. Here L3− is the deprotonated form of 2,6-bis[{{(1-hydroxy-2-methylpropan-2-yl)(pyridine-2-ylmethyl)}amino}methyl]-4-methylphenol. Complex 1 crystallizes in the cubic system, space group Fd-3c, with unit-cell parameters a = b = c = 43.320(5) A, Z = 48, whereas complex 2 crystallizes in the space group I41/a in the tetragonal crystal syst…
Road Functional Classification Using Pattern Recognition Techniques
2019
The existing international standards suggest a methodology to assign a specific functional class to a road, by the values of some features, both geometrical and use-related. Sometimes, these characteristics are in contrast with each other and direct the analyst towards conflicting classes for a road or, worse, one or more of these features vary heterogeneously along the road. In these conditions, the analyst assigns the class that, by his capability and experience, he retains the most appropriate, in a very subjective way. On the contrary, the definition of an automatic procedure assuring an objective identification of the most appropriate functional class for each road would be desirable. …
Why buying functional foods? Understanding spending behaviour through structural equation modelling
2013
Abstract The market for functional foods has been growing steadily in recent years, as it is linked to a healthier diet and adds value to food products. However, more information regarding aspects that influence functional food (FF) spending behaviour is needed to gain a better understanding of what underlies FF choice and avoid product failure. The objective of this study was to build a structural equation model of Spaniards' FF spending behaviour, based on individual characteristics such as satisfaction with life, decision-making styles, gender, age and some attitudes towards food choice. This required prior validation of the functional food questionnaire for a Spanish context, which was …
Why have consumers opposed, postponed, and rejected Innovations during a pandemic? A Study of mobile payment Innovations
2021
The highly infectious nature of the COVID-19 virus has made the use of contactless payment methods a health exigency. Yet, consumers are resisting using mobile payments (m-payments) during the pandemic, a confounding behavior that needs to be better understood. The present study explicates this behavior by examining consumer resistance to m-payments during the COVID-19 pandemic. In addition, it provides more granular findings by measuring three levels of resistance/non-adoption, namely, postponement, opposition, and rejection. In this way, the study adds depth to the literature, which has largely examined resistance at an aggregate level to yield generic findings. Toward this end, the study…