Search results for "Delocalized electron"
showing 10 items of 158 documents
Computational study of water adsorption on halloysite nanotube in different pH environments
2020
Abstract The comprehension of structural and energetic features of halloysite nanotube (HNT) in different chemical environments plays a crucial role in developing new HNT based materials. So far these aspects were investigated by means of laboratory techniques that hardly are able to provide hints at atomistic level of detail. Our investigation aims to obtain such accurate informations through density functional theory calculations on HNT models, in order to figure out the most stable forms of HNT under different pH conditions. It turns out that, at low pH, the preferred protonation sites are located in the inner aluminic surface while in alkaline medium the silicic layer can show delocaliz…
Polynitrile anions as ligands: From magnetic polymeric architectures to spin crossover materials
2010
International audience; The use of polynitrile anions as ligands (L) either alone or in combination with neutral co-ligands (L′) is a very promising and appealing strategy to get molecular architectures with different topologies and dimensionalities thanks to their ability to coordinate and bridge metal ions in many different ways. The presence of several potentially coordinating nitrile groups (or even other donor groups as –OH, –SH or –NH2), their rigidity and their electronic delocalization allow the synthesis of original magnetic high dimensional coordination polymers with transition metals ions. Furthermore, these ligands have shown coordinating and bridging capabilities in novel discr…
TCNQ radical salts containing magnetic complexes: Different interaction modes of TCNQ with Copper tetraazamacrocycles
1997
Abstract This work is devoted to the study of compounds [M(N 4 )](TCNQ) n , where N 4 = saturated or unsaturated tetraazamacrocycles, TCNQ= 7,7,8,8-tetracyanoquinodimethane, n= 2, 3. The metal is coordinated to two TCNQ groups only when there is coordinative unsaturation on it. When n= 2 all the TCNQ units are radical anions and no charge delocalization is observed. In the compounds with n= 3 only 2 3 of the TCNQ are negatively charged and a greater charge delocalization is possible. This delocalization only appears when none of the TCNQ's are coordinated to the metal and it is reflected in the higher conductivity values obtained in the solid state.
Annealing of color centers in LiBaF 3
2002
Results of the glow rate technique to analyze the activation energy of thermostimulated annealing of X-ray created F -type color centers in LiBaF 3 crystals are presented, showing pure and containing oxygen centers. It is shown that depending on the impurity composition two alternative mechanisms are involved in the annealing of color centers. It is proposed that either the anion vacancy governed migration of F -centers resulting in recombination with complementary defects, or the thermal delocalization of radiation created fluorine ( F i ) interstitials captured by anti-structure defects followed by recombination with all kinds of complementary F -type centers are responsible for the recom…
Effects of Indistinguishability in a System of Three Identical Qubits
2019
Quantum correlations of identical particles are important for quantum-enhanced technologies. The recently introduced non-standard approach to treat identical particles [G. Compagno et al., Phil. Trans. R. Soc. A 376, 20170317 (2018)] is here exploited to show the effect of particle indistinguishability on the characterization of entanglement of three identical qubits. We show that, by spatially localized measurements in separated regions, three independently-prepared separated qubits in a pure elementary state behave as distinguishable ones, as expected. On the other hand, delocalized measurements make it emerge a measurement-induced entanglement. We then find that three independently-prepa…
From Pentalene to Dicyclopenta[b,g]naphthalene, or the Change towards Delocalized Structures
2005
Lining triples-corrected coupled-cluster methods as well as other high-level theoretical approximations, the optimized parameters and isomerization barriers of the family of compounds cyclopentadiene-(benzene) x -cyclopentadiene (x 0, 1, 2) are computed. In contrast to previous studies, s-indacene presents a localized C 2 h geometry. Also, the localized structure of pentalene is found to be the most stable, but when two benzene rings are intercalated between the five-member rings of pentalene, the resulting molecule preferably adopts a delocalized D 2 h conformation.
In situ XAFS study of phase transitions and hydrogen intercalation in WO3-MoO3 system
1995
Abstract The WO 3 -MoO 3 system has several reconstructive and displacive phase transitions which can be induced by temperature and/or by change of stoichiometry or valence state of metal ions under hydrogen intercalation. We have studied in situ the local electronic and structural changes arising in WO 3 -MoO 3 system with hydrogen intercalation and temperature. In situ XAFS measurements at the Mo K and W L 3 edges in H y Mo x W 1− x O 3 compounds, performed at different hydrogen intercalation level and temperatures (from RT to 500°C), allowed us to determine the rearrangement in the first and second coordination shells of Mo and W cations during phase transitions. It was found that hydrog…
Imaging standing surface plasmons by photon tunneling
2005
We present a direct method for optically exciting and imaging delocalized standing surface plasmons in thin metal films. We show theoretically that when imaging the field of the plasmons with a photon scanning tunneling microscope, the presence of the dielectric probe has a negligible effect on the surface modes of the metal film. We demonstrate that plasmon interference can be sustained in arbitrarily large regions of the metal film in comparison to the excitation wavelength. This knowledge can be important when seeking the relative distance between two scattering centers such as the presence of micron or submicron structures.
A Wigner molecule at extremely low densities: a numerically exact study
2019
In this work we investigate Wigner localization at very low densities by means of the exact diagonalization of the Hamiltonian. This yields numerically exact results. In particular, we study a quasi-one-dimensional system of two electrons that are confined to a ring by three-dimensional gaussians placed along the ring perimeter. To characterize the Wigner localization we study several appropriate observables, namely the two-body reduced density matrix, the localization tensor and the particle-hole entropy. We show that the localization tensor is the most promising quantity to study Wigner localization since it accurately captures the transition from the delocalized to the localized state an…
Level statistics and Anderson delocalization in two-dimensional granular materials
2020
Contrary to the theoretical predictions that all waves in two-dimensional disordered materials are localized, Anderson localization is observed only for sufficiently high frequencies in an isotropically jammed two-dimensional disordered granular packing of photoelastic disks. More specifically, we have performed an experiment in analyzing the level statistics of normal mode vibrations. We observe delocalized modes in the low-frequency boson-peak regime and localized modes in the high frequency regime with the crossover frequency just below the Debye frequency. We find that the level-distance distribution obeys Gaussian-Orthogonal-Ensemble (GOE) statistics, i.e. Wigner-Dyson distribution, in…