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Electronic Correlations (electronic + correlation)
Kinds of Electronic Correlations Selected AbstractsInfluence of electron correlations on strong field ionization of calciumLASER PHYSICS LETTERS, Issue 1 2004E. Charron Abstract Non-perturbative time-dependent calculations of single and double ionization of a one-dimensional model of atomic calcium by short and intense laser pulses were performed at various wavelengths. The comparison of the probabilities calculated within a two-active electron (TAE) approach with those obtained using a single-active electron (SAE) approximation clearly demonstrates the crucial role played by the electronic correlation and by doubly excited states within this model, even for the formation of Ca+. Experimental and calculated energy spectra of the singlet states of Ca. The experimental values (b) are taken from [20], and the calculated values (a) on the left and (c) on the right correspond to the present SAE and TAE models respectively. (© 2004 by HMS Consultants. Inc. Published exclusively by WILEY-VCH Verlag GmbH & Co.KGaA) [source] Non-empirical calculations of NMR indirect carbon,carbon coupling constants.MAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2003Part 4: Bicycloalkanes Abstract A systematic study of the one-bond and long-range J(C,C), J(C,H) and J(H,H) in the series of nine bicycloalkanes was performed at the SOPPA level with special emphasis on the coupling transmission mechanisms at bridgeheads. Many unknown couplings were predicted with high reliability. Further refinement of SOPPA computational scheme adjusted for better performance was carried out using bicyclo[1.1.1]pentane as a benchmark to investigate the influence of geometry, basis set and electronic correlation. The calculations performed demonstrated that classical ab initio SOPPA applied with the locally dense Dunning's sets augmented with inner core s-functions used for coupled carbons and Sauer's sets augmented with tight s-functions used for coupled hydrogens performs perfectly well in reproducing experimental values of different types of coupling constants (the estimated reliability is ca 1,2 Hz) in relatively large organic molecules of up to 11 carbon atoms. Additive coupling increments were derived for J(C,C), J(C,H) and J(H,H) based on the calculated values of coupling constants within SOPPA in the model bicycloalkanes, in reasonably good agreement with the known values obtained earlier on pure empirical grounds. Most of the bridgehead couplings in all but one bicycloalkane appeared to be essentially additive within ca 2,3 Hz while bicyclo[1.1.1]pentane demonstrated dramatic non-additivity of ,14.5 Hz for J(C,C), +16.6 Hz for J(H,H) and ,5.5 Hz for J(C,H), in line with previous findings. Non-additivity effects in the latter compound established at the SOPPA level should be attributed to the through-space non-bonded interactions at bridgeheads due to the essential overlapping of the bridgehead rear lobes which provides an additional and effective non-bonding coupling path for the bridgehead carbons and their protons in the bicyclopentane framework. Copyright © 2003 John Wiley & Sons, Ltd. [source] Reaction pathways of propene pyrolysisJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2010Yena Qu Abstract The gas-phase reaction pathways in preparing pyrolytic carbon with propene pyrolysis have been investigated in detail with a total number of 110 transition states and 50 intermediates. The structure of the species was determined with density functional theory at B3PW91/6-311G(d,p) level. The transition states and their linked intermediates were confirmed with frequency and the intrinsic reaction coordinates analyses. The elementary reactions were explored in the pathways of both direct and the radical attacking decompositions. The energy barriers and the reaction energies were determined with accurate model chemistry method at G3(MP2) level after an examination of the nondynamic electronic correlations. The heat capacities and entropies were obtained with statistical thermodynamics. The Gibbs free energies at 298.15 K for all the reaction steps were reported. Those at any temperature can be developed with classical thermodynamics by using the fitted (as a function of temperature) heat capacities. It was found that the most favorable paths are mainly in the radical attacking chain reactions. The chain was proposed with 26 reaction steps including two steps of the initialization of the chain to produce H and CH3 radicals. For a typical temperature (1200 K) adopted in the experiments, the highest energy barriers were found in the production of C3 to be 203.4 and 193.7 kJ/mol. The highest energy barriers for the production of C2 and C were found 174.1 and 181.4 kJ/mol, respectively. These results are comparable with the most recent experimental observation of the apparent activation energy 201.9 ± 0.6 or 137 ± 25 kJ/mol. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Ab-initio simulations of materials using VASP: Density-functional theory and beyondJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2008Jürgen Hafner Abstract During the past decade, computer simulations based on a quantum-mechanical description of the interactions between electrons and between electrons and atomic nuclei have developed an increasingly important impact on solid-state physics and chemistry and on materials science,promoting not only a deeper understanding, but also the possibility to contribute significantly to materials design for future technologies. This development is based on two important columns: (i) The improved description of electronic many-body effects within density-functional theory (DFT) and the upcoming post-DFT methods. (ii) The implementation of the new functionals and many-body techniques within highly efficient, stable, and versatile computer codes, which allow to exploit the potential of modern computer architectures. In this review, I discuss the implementation of various DFT functionals [local-density approximation (LDA), generalized gradient approximation (GGA), meta-GGA, hybrid functional mixing DFT, and exact (Hartree-Fock) exchange] and post-DFT approaches [DFT + U for strong electronic correlations in narrow bands, many-body perturbation theory (GW) for quasiparticle spectra, dynamical correlation effects via the adiabatic-connection fluctuation-dissipation theorem (AC-FDT)] in the Vienna ab initio simulation package VASP. VASP is a plane-wave all-electron code using the projector-augmented wave method to describe the electron-core interaction. The code uses fast iterative techniques for the diagonalization of the DFT Hamiltonian and allows to perform total-energy calculations and structural optimizations for systems with thousands of atoms and ab initio molecular dynamics simulations for ensembles with a few hundred atoms extending over several tens of ps. Applications in many different areas (structure and phase stability, mechanical and dynamical properties, liquids, glasses and quasicrystals, magnetism and magnetic nanostructures, semiconductors and insulators, surfaces, interfaces and thin films, chemical reactions, and catalysis) are reviewed. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Conductance through a redox system in the Coulomb blockade regime: Many-particle effects and influence of electronic correlationsPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 1-2 2010Sabine Tornow Abstract We investigate the transport characteristics of a redox system weakly coupled to leads in the Coulomb blockade regime. The redox system comprises a donor and acceptor separated by an insulating bridge in a solution. It is modeled by a two-site extended Hubbard model which includes on-site and inter-site Coulomb interactions and the coupling to a bosonic bath. The current,voltage characteristics is calculated at high temperatures using a rate equation approach. For high voltages exceeding the Coulomb repulsion at the donor site the calculated transport characteristics exhibit pronounced deviations from the behavior expected from single-electron transport. Depending on the relative sizes of the effective on-site and inter-site Coulomb interactions on one side and the reorganization energy on the other side we find either negative differential resistance or current enhancement. Schematic view of the redox system with donor (D) and acceptor (A) coupled to the leads L and R. The electronic degrees of freedom of the DA system are coupled to the environment comprising internal vibrations and the solvent dynamics. The current is calculated as a function of the bias voltage Vb and gate voltage Vg. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Forward scattering peak in the electron,phonon interaction and impurity scattering of cuprate superconductorsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2005M. L. Kuli Abstract The important role of the electron,phonon interaction (EPI) in explaining the normal state properties and pairing mechanism in high- Tc superconductors (HTSC) is discussed. A number of experiments are analyzed such as: dynamical conductivity, Raman scattering, neutron scattering, ARPES, tunnelling measurements, and etc. They give convincing evidence that the EPI dominantly contributes to pairing in HTSC oxides. Strong electronic correlations cause the forward scattering peak (FSP) in the EPI and in the non-magnetic impurity potential. The theory based on the FSP (whatever is its origin) explains several puzzling experimental results in ARPES and transport: (1) much smaller transport coupling constant than the pairing one (,tr , ,ph); (2) the ARPES non-shift puzzle , where the nodal kink at 70 meV is unshifted in the superconducting state while the anti-nodal one at 40 meV is shifted; (3) d-wave superconductivity due to the EPI; (4) robustness of d-wave pairing in the presence of nonmagnetic impurities; (5) collapse of the elastic scattering rate near the anti-nodal point in the superconducting state; (6) anomalous temperature dependence of the Hall angle in optimally doped HTSC. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electronic transport through large quantum dots in the Kondo regimePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003P. Stefa Abstract Conductance through a large two-level quantum dot is investigated theoretically in the strong coupling regime. In large quantum dots the separation between discrete levels becomes smaller than the level width due to strong hybridization with electrodes. In such circumstances, apart from strong electronic correlations in the quantum dot, the indirect interaction between both the spatial levels comes into play. It takes place in lateral quantum dots, where the spatial level index is not conserved during the hybridization process with electrodes. This interaction shifts the Kondo resonance peak in the density of states out of the Fermi surface and alters its intensity. This feature can be observed in the differential conductance dependence vs. bias voltage. The virtual inter-level mixing is suppressed for temperatures above the Kondo temperature of the system. The results of theoretical predictions are compared with the results of experimental conductance measurements performed on large quantum dots and some non-typical conductance features are clarified. [source] Influence of electronic correlations on the frequency-dependent hopping transport in Si:PPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2008Elvira Ritz Abstract At low energy scales charge transport in the insulating Si:P is dominated by activated hopping between the localized donor electron states. Thus, theoretical models for a disordered system with electron-electron interaction are appropriate to interpret the electric conductivity spectra. With a newly developed technique we have measured the complex broadband microwave conductivity of Si:P from 100 MHz to 5 GHz in a broad range of phosphorus concentration n /nc from 0.56 to 0.95 relative to the critical value nc = 3:5 × 1018 cm,3 corresponding to the metal-insulator transition driven by doping. At our base temperature of T = 1.1 K the samples are in the zero-phonon regime where they show a super-linear frequency dependence of the conductivity indicating the influence of the Coulomb gap in the density of the impurity states. At higher doping n , nc, an abrupt drop in the conductivity power law ,1(,) , ,, is observed. The dielectric function ,1 increases upon doping following a power law in (1 , n /nc). Dynamic response at elevated temperatures has also been investigated. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Unconventional superconductivity and magnetism in Sr2RuO4 and related materialsANNALEN DER PHYSIK, Issue 3 2004I. Eremin Abstract We review the normal and superconducting state properties of the unconventional triplet superconductor Sr2RuO4 with an emphasis on the analysis of the magnetic susceptibility and the role played by strong electronic correlations. In particular, we show that the magnetic activity arises from the itinerant electrons in the Ru d -orbitals and a strong magnetic anisotropy occurs (,+- < ,zz) due to spin-orbit coupling. The latter results mainly from different values of the g -factor for the transverse and longitudinal components of the spin susceptibility (i.e. the matrix elements differ). Most importantly, this anisotropy and the presence of incommensurate antiferromagnetic and ferromagnetic fluctuations have strong consequences for the symmetry of the superconducting order parameter. In particular, reviewing spin fluctuation-induced Cooper-pairing scenario in application to Sr2RuO4 we show how p -wave Cooper-pairing with line nodes between neighboring RuO2 -planes may occur. We also discuss the open issues in Sr2RuO4 like the influence of magnetic and non-magnetic impurities on the superconducting and normal state of Sr2RuO4. It is clear that the physics of triplet superconductivity in Sr2RuO4 is still far from being understood completely and remains to be analyzed more in more detail. It is of interest to apply the theory also to superconductivity in heavy-fermion systems exhibiting spin fluctuations. [source] | |||||||||||||