Search results for "Quantum"
showing 10 items of 9714 documents
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 …
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-…
Valence electronic structure of C60: Theoretical analysis of photoemission data
1993
Abstract We present a theoretical investigation of the valence band photoemission spectra of C 60 using the nonempirical valence effective Hamiltonian (VEH) method. The VEH-DOVS curves calculated for the C 60 molecule are found to be in excellent agreement with synchrotron-radiation photoemission spectra reported for C 60 films. A detailed interpretation of all the photoemission bands is performed in the light of the VEH results.
Theoretical study on the effect of backbone conformation on the electronic structure of poly(di-n-butylsilane)
1993
Abstract We present the results of valence effective Hamiltonian (VEH) calculations on the electronic structure of poly(di-n-butylsilane) in its all-trans and 7/3 conformations. The band structure of all-trans conformation is analyzed in detail and the effects of the backbone conformation on the electronic and optical properties are studied. The VEH results for the 2/1 and 7/3 conformations are in excellent quantitative agreement with photoemission and UV-absorption data and show the reliability of the VEH method to deal with organopolysilanes.
Spin Switching in Molecular Quantum Cellular Automata Based on Mixed-Valence Tetrameric Units
2016
In this article we focus on the study of spin effects in a single square-planar mixed-valence cell comprising two electrons and in coupled molecular cells for quantum cellular automata. Using the vibronic model we demonstrate that the polarizabilities of the cell are different in spin-singlet and spin-triplet states of the electronic pair. Based on this inference the concept of spin switching in molecular quantum cellular automata is proposed, and the conditions under which this effect is feasible are derived. In order to reveal these conditions we have performed a series of quantum-mechanical calculations of the vibronic energy levels of the isolated cell and of the cell subjected to the e…
Pressure Dependence of the Band Gaps and Charge Densities in Si
1994
The empirical local and nonlocal pseudopotentials of Si which can describe the electronic energy structure over a wide energy range of more than 20 eV from the bottom of the valence band is determined for different pressures. The nonlocality of the potential is described by the Gaussian model. The predictions for the linear and quadratic pressure coefficients are consistent with the experiment. The valence charge densities of Si under high pressure are studied. The forbidden X-ray factor F(222) is very stable under pressure and changes by less than 3% under volume changes of the order of 5%.
Self-trapping of charge polarized states in four-dot molecular quantum cellular automata: bi-electronic tetrameric mixed-valence species
2014
Abstract Our interest in this article is prompted by the problem of the vibronic self-trapping of charge polarized states in the four-dot molecular quantum cellular automata (mQCA), a paradigm for nanoelectronics, in which binary information is encoded in charge configuration of the mQCA cell. We report the evaluation of the electronic states and the adiabatic potentials of mixed-valence (MV) systems in which two electrons (or holes) are shared among four sites. These systems are exemplified by the two kinds of tetra–ruthenium (2Ru(II)+ 2Ru(III)) clusters (assembled as two coupled Creutz–Taube dimers) for which molecular implementation of mQCA was proposed. The tetra–ruthenium clusters incl…
Problem of the magnetic anisotropy in orbitally degenerate exchange and mixed-valence clusters
2003
Abstract This contribution summarizes the results obtained in the problem of orbital degeneracy of the metal ions in exchange coupled and mixed-valence (MV) clusters. The theory of the double exchange is generalized and the orbitally degenerate systems are considered. The orbitally dependent double exchange parameter is deduced for the singlet–triplet and triplet–triplet transition metal pairs in three high-symmetric topologies. A new effective Hamiltonian of the magnetic exchange between the ions with unquenched orbital angular momenta is discussed. The technique of the irreducible tensor operators is applied to the problem of the kinetic exchange in these kind of metal clusters. Strong ma…
Theoretical calculations on the valence electronic structure of naphthalocyanine: comparison with experimental photoemission data
1993
Abstract We present a theoretical investigation of the electronic structure of metal-free 2,3-naphthalocyanine (2,3-H2Nc) using the valence effective Hamiltonian (VEH) technique. The VEH-DOVS curves obtained for 2,3-H2Nc are correlated with those calculated for naphthalene molecule and a one-to-one correspondence is found. From the electronic structure standpoint, naphthalocyanine has to be viewed as formed by joining four naphthalene moieties to the central carbon-nitrogen ring. An excellent quantitative agreement is found between VEH-DOVS curves and experimental photoemission data.
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…