Search results for "Valence"
showing 10 items of 2732 documents
VEH electronic structure of Si60
1993
Abstract We present a valence effective Hamiltonian (VEH) theoretical investigation on the electronic structure of Si60. The VEH one-electron energy level distribution calculated for Si60 is used to predict the ionization potential (7.86 eV), electron affinity (6.62 eV) and HOMO-LUMO energy gap (1.24 eV) of Si60. We also report the first allowed electronic transitions of Si60. The results are compared with other theoretical levels and with those calculated for C60.
Mixed-Valence Molecular Unit for Quantum Cellular Automata: Beyond the Born-Oppenheimer Paradigm through the Symmetry-Assisted Vibronic Approach.
2016
In this article, we focus on the electron-vibrational problem of the tetrameric mixed-valence (MV) complexes proposed for implementation as four-dot molecular quantum cellular automata (mQCA).1 Although the adiabatic approximation explored in ref 2 is an appropriate tool for the qualitative analysis of the basic characteristics of mQCA, like vibronic trapping of the electrons encoding binary information and cell-cell response, it loses its accuracy providing moderate vibronic coupling and fails in the description of the discrete pattern of the vibronic levels. Therefore, a precise solution of the quantum-mechanical vibronic problem is of primary importance for the evaluation of the shapes o…
A theoretical determination of the electronic spectrum of formaldehyde
1995
The electronically excited states of formaldehyde are examined by means of multiconfigurational second-order perturbation (CASPT2) theory with extended ANO-type basis sets. The calculations comprised five valence excited states plus all singlet 3s, 3p, and 3d members of the Rydberg series converging on the first ionization. The computed vertical excitation energies were found to be within 0.2 eV of the available experimental energies. Full geometry optimization has been performed for five valence excited states. Assuming a planar geometry, the “0-0” transition for the valence1A1(π → π*) state is calculated to appear near 7.9 eV, close to the (n y → 3p) region. This state is, however, not pl…
Origin of the Paramagnetic Properties of the Mixed‐Valence Polyoxometalate [GeV 14 O 40 ] 8– Reduced by Two Electrons: Wave Function Theory and Model…
2009
The aim of the work is to give an explanation of the magnetic properties of a mixed-valence [GeV14O40]8– polyoxometalate reduced by two electrons, which, in contrast to what happens in other two-electron-reduced polyoxometalates, does not show any magnetic coupling between the two unpaired electrons. For this purpose, a quantitative evaluation of the microscopic electronic parameters (electron transfer, magnetic coupling, magnetic orbital energy, and Coulomb repulsion) of the mixed-valence polyoxometalate cluster is performed. The parameters are extracted from valence-spectroscopy large configuration interaction (CI) calculations on embedded fragments. Then, these parameters are used in an …
Theoretical study of the electronic spectrum of p-benzoquinone
1999
The electronic excited states of p-benzoquinone have been studied using multiconfigurational second-order perturbation theory (CASPT2) and extended atomic natural orbital (ANO) basis sets. The calculation of the singlet–singlet and singlet–triplet transition energies comprises 19 valence singlet excited states, 4 valence triplet states, and the singlet 3s,3p, and 3d members of the Rydberg series converging to the first four ionization limits. The computed vertical excitation energies are found to be in agreement with the available experimental data. Conclusive assignments to both valence and Rydberg states have been performed. The main features of the electronic spectrum correspond to the π…
Full configuration interaction calculation of the low lying valence and Rydberg states of BeH
2007
The all-electron full configuration interaction (FCI) vertical excitation energies for some low lying valence and Rydberg excited states of BeH are presented in this article. A basis set of valence atomic natural orbitals has been augmented with a series of Rydberg orbitals that have been generated as centered onto the Be atom. The resulting basis set can be described as 4s2p1d/2s1p (Be/H) + 4s4p3d. It allows to calculate Rydberg states up to n= {3,4,5} of the s, p, and d series of Rydberg states. The FCI vertical ionization potential for the same basis set and geometry amounts to 8.298 eV. Other properties such as FCI electric dipole and quadrupole moments and FCI transition dipole and qua…
Theoretical Study of the Electronic Spectrum of Imidazole
1996
The complete active space (CAS) self-consistent field (SCF) method and multireference second-order perturbation theory (CASPT2) have been used to study the electronic spectrum of imidazole and the imidazolium ion. The calculations comprise a large number of, both singlet and triplet, valence and Rydberg excited states. A newly developed continuum model has been used to compute solvatochromic shifts. In the gas phase the first and second π → π* excited singlet valence states of imidazole are computed at 6.72 and 7.15 eV, and they shift to 6.32 and 6.53 eV upon solvation. The gas-phase values are somewhat too large (≈0.3 eV) due to an erroneous valence−Rydberg mixing in the CASSCF wave functi…
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…
Correlation between oxidation states of transition metal ions and variation of the coercivity in mixed-valence defect spinel ferrites
1997
Abstract Due to the very high dispersion of mixed-valence spinel ferrites prepared by ‘soft chemistry’ it becomes possible to oxidize in the spinel lattice, not only ferrous ions but also different transition metal ions (Cr 3+ , Mn 2+ , Mn 3+ , Mo 3+ , Mo 4+ V 2+ , V 3+ , Cu + ), by ‘soft’ oxidation between 150 and 500°C, under formation of non-stoichiometric spinels cation vacancies. The oxidation state with the coordination and the oxidation temperature of the cations have been determined in coppermanganese ferrites by derivative thermogravimetry (DTG), based on the specific solid-state reactivity of cations in the redox reaction. For Co-modified non-stoichiometric spinels, which present…
Localisation vs. delocalisation in the dimeric mixed-valence clusters in the generalised vibronic model. Magnetic manifestations
1999
Abstract The problem of localisation–delocalisation in the dimeric mixed-valence clusters is considered in the framework of the generalised vibronic model. The model takes into account both the local vibrations on the metal sites (Piepho–Krausz–Schatz model) and the multicenter (molecular) vibrations changing the intermetallic distances (as suggested by Piepho). In the framework of the semiclassical adiabatic approach the potential surfaces are analysed and different kinds of localised and delocalised states are found. On the basis of the calculated degrees of the localisation the conventional Robin and Day classification of mixed-valence compounds is reconsidered in view of the generalised…