Search results for "Delocalized electron"
showing 10 items of 158 documents
Role of the electron transfer and magnetic exchange interactions in the magnetic properties of mixed-valence polyoxovanadate complexes.
2008
International audience; Modeling the properties of high-nuclearity, high-electron-population, mixed-valence (MV) magnetic systems remains one of the open challenges in molecular magnetism. In this work, we analyze the magnetic properties of a series of polyoxovananadate clusters of formula [V 18O 42] (12-) and [V 18O 42] (4-). The first compound is a fully localized spin cluster that contains 18 unpaired electrons located at the metal sites, while the second one is a MV cluster with 10 unpaired electrons largely delocalized over the 18 metal sites. A theoretical model that takes into account the interplay between electron transfer and magnetic exchange interactions is developed to explain t…
A symmetry adapted approach to the dynamic Jahn-Teller problem: Application to mixed-valence polyoxometalate clusters with keggin structure
2012
In this article, we present a symmetry-adapted approach aimed to the accurate solution of the dynamic vibronic problem in large scale Jahn-Teller (JT) systems. The algorithm for the solution of the eigen-problem takes full advantage of the point symmetry arguments. The system under consideration is supposed to consist of a set of electronic levels mixed by the active JT and pseudo JT vibrational modes. Applying the successive coupling of the bosonic creation operators, we introduce the irreducible tensors that are called multivibronic operators. Action of the irreducible multivibronic operators on the vacuum state creates the vibrational symmetry adapted basis that is subjected to the Gram-…
Mixed‐valence trinuclear manganese clusters : Influence of the electronic transfer on the magnetic properties
1990
The magnetic behavior of mixed‐valence trinuclear clusters d4‐d4‐d5 is discussed on the basis of a model which takes into account valence delocalization and Heisenberg exchange. This model considers the competing effect between the electronic transfer and the localization of the extra electron due to an asymmetry of the triangular entity. The magnetic properties of the mixed‐valence oxo‐centered Mn(II)‐Mn(III)‐Mn(III) complexes formulated as Mn3O(O2CR)6L3 (R=Me, L=pyridine) are discussed on the basis of the developed model, supporting a significant intramolecular electron transfer. A comparison of these results to those previously reported by assuming a valence‐trapped model is given. Carlo…
Magnetic mixed-valence d2-d1-d1 trimers with partial electron delocalization: vibronic coupling and magnetic properties
1993
Abstract The energy levels and magnetic properties of a triangular mixed-valence cluster d1-d1-d2 with electron delocalization in a pair of sites are examined from a model that takes into account electron transfer, magnetic exchange, and vibronic coupling. We show that the electron transfer process involves besides the usual double-exchange parameter, and additional parameter referred to as exchange transfer. This last parameter accounts for the interaction between the moving electron of the mixed valence pair and the electron localized in the third side. We notice that the role of double exchange is to stabilize a ferromagnetic alignment of the spins on the mixed-valence pair. A comparison…
Electric Field Generation and Control of Bipartite Quantum Entanglement between Electronic Spins in Mixed Valence Polyoxovanadate [GeV14O40]8–
2017
As part of the search for systems in which control of quantum entanglement can be achieved, here we consider the paramagnetic mixed valence polyoxometalate K2Na6[GeV14O40]·10H2O in which two electrons are delocalized over the 14 vanadium ions. Applying a homogeneous electric field can induce an antiferromagnetic coupling between the two delocalized electronic spins that behave independently in the absence of the field. On the basis of the proposed theoretical model, we show that the external field can be used to generate controllable quantum entanglement between the two electronic spins traveling over a vanadium network of mixed valence polyoxoanion [GeV14O40]8–. Within a simplified two-lev…
Mixed-valence polyoxometalate clusters. III. Vibronic problem for the 2-electron reduced heteropoly blue with the Keggin structure
1995
Abstract A general approach to the vibronic problem of delocalized electronic pairs in mixed-valence compounds is developed and applied to understand the ways of electron delocalization in dodecanuclear polyoxometalate clusters containing two moving electrons. The interplay between electronic and vibronic interactions is examined. The electronic spectrum is shown to consist of two spin triplets 3 T 1 and 3 T 2 and three spin singlets 1 A 1 , 1 E and 1 T 2 levels determined by the double-transfer processes (parameter P ). Jahn-Teller and pseudo-Jahn-Teller problems ( 3 T 1 + 3 T 2 ) ⊗ ( e + t 2 ) and ( 1 A 1 + 1 E + 1 T 2 ) ⊗ ( e + t 2 ) have been considered in the framework of the Piepho-Kr…
Mixed-valence polyoxometalate clusters. I. Delocalization of electronic pairs in dodecanuclear heteropoly blues with keggin structure
1995
Abstract The problem of delocalization of a pair of electrons over dodecanuclear polyoxometalate clusters with the Keggin structure is considered with the aim of explaining the spin pairing in these multi-nuclear mixed-valence systems. A general approach that considers the Coulomb interactions between the two delocalized electrons, as well as the single and double electron transfer processes which can be operative in delocalization of the electronic pairs is developed. The new approach is based on the site-symmetry concept which makes possible a group theoretical classification for the delocalized states of electronic pairs. This procedure proves to be very efficient in the calculation of t…
Modelling electric field control of the spin state in the mixed-valence polyoxometalate [GeV14O40]8−
2013
International audience; : The two-electron reduced mixed-valence polyoxometalate [GeV14O40](8-) presents an unusual paramagnetic behaviour as a consequence of the partial trapping of these electrons. The effect of applying an electric field is that of inducing antiferromagnetic coupling between the two delocalized electronic spins.
Electrically switchable magnetic molecules: inducing a magnetic coupling by means of an external electric field in a mixed-valence polyoxovanadate cl…
2015
International audience; Herein we evaluate the influence of an electric field on the coupling of two delocalized electrons in the mixed-valence polyoxometalate (POM) [GeV14 O40 ](8-) (in short V14 ) by using both a t-J model Hamiltonian and DFT calculations. In absence of an electric field the compound is paramagnetic, because the two electrons are localized on different parts of the POM. When an electric field is applied, an abrupt change of the magnetic coupling between the two delocalized electrons can be induced. Indeed, the field forces the two electrons to localize on nearest-neighbors metal centers, leading to a very strong antiferromagnetic coupling. Both theoretical approaches have…
Metallic subnanometer porous silicon: A theoretical prediction
2021
In the present work, T-Si, a silicon-based counterpart of T-carbon, has been designed with the aid of density functional theory (DFT) calculations. Its stability has been fully confirmed from energetic, mechanical, lattice dynamic, and thermodynamic aspects. Due to the space extrusion, the delocalized electrons on the ${\mathrm{Si}}_{4}$ tetrahedrons are squeezed onto the inter-tetrahedron $\mathrm{Si}\ensuremath{-}\mathrm{Si}$ bonds, which therefore leads T-Si to be metallic. Furthermore, the electronic conductivity of this new material has also been predicted and discussed in this work. This new silicon allotrope with a low density of $0.869\mathrm{g}/{\mathrm{cm}}^{3}$ can even floats on…