Strong electron correlation

The computation of furoxans (l,2,5-oxadiazole-2-oxides) is very demanding. Very strong electron correlation effects hamper a proper treatment of this class of molecules. With respect to the geometric parameters, it is the endocyclic N—O bond that can be treated reliably either at the B3-LYP or at the MP4(SDQ) level [99MI1 ]. Table II demonstrates the problems associated with the exact determination of this bond length. 

Schipper, P. R. T., Gritsenko, O. V., Baerends, E. J., 1998a, One-Determinantal Pure State versus Ensemble Kohn-Sham Solutions in the Case of Strong Electron Correlation CH2 and C2 , Theor. Chem. Acc., 99, 329. 

The resistivity of YbNi2B2C decreases monotonically with decreasing temperature (see fig. 49), but drops pronouncedly below 50 K (Yatskar et al. 1996 Dhar et al. 1996). A quadratic temperature dependence of the resistivity was found below 1.5 K which is a characteristic feature of strong-electron correlation (Yatskar et al. 1996). 

It was found that because of the strong electron correlation the phonon-induced charge transfer depends on the spin. Consequently the phonon modifies the spin correlation and spin dynamics [12]. In the strongly correlated electron systems phonons interact not only with charge, but also with spins. 

The different emission products which are possible after photoionization with free atoms lead to different experimental methods being used for example, electron spectrometry, fluorescence spectrometry, ion spectrometry and combinations of these methods are used in coincidence measurements. Here only electron spectrometry will be considered. (See Section 6.2 for some reference data relevant to electron spectrometry.) Its importance stems from the rich structure of electron spectra observed for photoprocesses in the outermost shells of atoms which is due to strong electron correlation effects, including the dominance of non-radiative decay paths. (For deep inner-shell ionizations, radiative decay dominates (see Section 2.3).) In addition, the kinetic energy of the emitted electrons allows the selection of a specific photoprocess or subsequent Auger or autoionizing transition for study. 

The large ratio a2p(discr. sat)/<72p quantifies the remarkable intensity of 2p satellites and is a direct indicator for strong electron correlation effects in 2p photoionization. 

The aim of this work is to demonstrate that the above-mentioned unusual properties of cuprates can be interpreted in the framework of the t-J model of a Cu-O plane which is a common structure element of these crystals. The model was shown to describe correctly the low-energy part of the spectrum of the realistic extended Hubbard model [4], To take proper account of strong electron correlations inherent in moderately doped cuprate perovskites the description in terms of Hubbard operators and Mori s projection operator technique [5] are used. The self-energy equations for hole and spin Green s functions obtained in this approach are self-consistently solved for the ranges of hole concentrations 0 < x < 0.16 and temperatures 2 K< T <1200 K. Lattices with 20x20 sites and larger are used. 

Figure 1. The effect of strong electron correlations on the low-temperature specific heat coefficient y.

Beznosjuk S.A., Minaev B.F., Dajanov R.D., Muldachmetov Z.M. (1990) Approximating quasiparticle density functional calculations of small active clusters strong electron correlation effects, Int. J. Quant. Chem. 38(6), 779-797. 

In the Hubbard model it was found that phonon-induced charge transfer is spin polarized because of strong electron correlation. The dynamics of spins is strongly modified by the Cu-0 bond-stretching phonons, and the spin excitations are generally greatly softened by phonons10. This must be related... 

To derive the dynamical spin susceptibility in the superconducting state we use the method suggested by Hubbard and Jain[15] that allows to take into account strong electronic correlations. First we add the external magnetic field applied along c-axis into the effective Hamiltonian... 

This is a central result of our paper. Here, xo(q> °>) is the usual BCS-like Lind-hard response function, n(q, co) and Z(q, co) result from the strong electronic correlation effects. In the normal state the expression for n(q, co) has been obtained by Hubbard and Jain [15]. In the superconducting state it is given by... 

The bonding of Sr-O is very weak covalent. Mo-O is the strongest covalent. In Fe-O-Mo covalent bonding appears as a whole resulting in strong electron correlation. 

Flowever, there is also a Curie-Weiss-like behavior at temperatures below 50 K in the two lower curves of Figure 6.6a and below about 150K in the two upper curves, which is indicative of electron correlation. Since Ti is to the left of the first transition period, relatively strong electron correlation in the Ti 3d orbitals would be expected. In fact, a linear dependency of the resistivity to (plots of p versus 7 were linear) was also reported in the metallic phases, supporting the presence of correlation effects. 

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