Search results for " function"
showing 10 items of 9395 documents
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.
Electronic Excitation in a Saturated Chain: An MS-CASPT2 Treatment of the Anti Conformer of n-Tetrasilane
2000
The singlet−singlet electronic spectrum of the anti conformer of n-tetrasilane has been studied using multiconfigurational wave functions (CASSCF), second-order perturbation theory (CASPT2), and its multi-state extension (MS-CASPT2), in conjunction with large ANO-type basis sets including Rydberg functions. The calculations include the 4s, 4p, and 3d members of the Rydberg series converging on the first ionization. Mixing of valence and Rydberg states observed in the CASSCF wave functions is not fully rectified by single-reference CASPT2 theory, whereas the MS-CASPT2 method separates the valence and Rydberg states effectively. At the MS-CASPT2 level, six valence excited states have been fou…
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…
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…
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…
Nonstationary response envelope probability densities of nonlinear oscillators
2006
The nonstationary random response of a class of lightly damped nonlinear oscillators subjected to Gaussian white noise is considered. An approximate analytical method for determining the response envelope statistics is presented. Within the framework of stochastic averaging, the procedure relies on the Markovian modeling of the response envelope process through the definition of an equivalent linear system with response-dependent parameters. An approximate solution of the associated Fokker-Planck equation is derived by resorting to a Galerkin scheme. Specifically, the nonstationary probability density function of the response envelope is expressed as the sum of a time-dependent Rayleigh dis…
One-dimensional nonlinear boundary value problems with variable exponent
2018
In this paper, a class of nonlinear differential boundary value problems with variable exponent is investigated. The existence of at least one non-zero solution is established, without assuming on the nonlinear term any condition either at zero or at infinity. The approach is developed within the framework of the Orlicz-Sobolev spaces with variable exponent and it is based on a local minimum theorem for differentiable functions.
Variable Selection with Quasi-Unbiased Estimation: the CDF Penalty
2022
We propose a new non-convex penalty in linear regression models. The new penalty function can be considered a competitor of the LASSO, SCAD or MCP penalties, as it guarantees sparse variable selection while reducing bias for the non-null estimates. We introduce the methodology and present some comparisons among different approaches.