Stereodivergent Total Synthesis of Δ9‐Tetrahydrocannabinols

All four stereoisomers of Δ⁹‐tetrahydrocannabinol (Δ⁹‐THC) were synthesized in concise fashion using stereodivergent dual catalysis. Thus, following identical synthetic sequences and applying identical reaction conditions to the same set of starting materials, selective access to the four stereoisomers of THC was achieved in five steps.     

Double fluctuations on the attractive Hubbard model: ladder approximation

We explore, for the first time, the effect of double fluctuations on both the diagonal and off-diagonal selfenergy. We use the T-Matrix equations below T _c , developed recently by the Zürich group (M.H. Pedersen et al) for the local pair attraction Hamiltonian. Here, we include as well the effect of fluctuations on the order parameter (beyond the BCS solution) up to second order in U/t. This is equivalent to approximating the effective interaction by U in the off-diagonal self-energy. For U/t = ?6.0, T/t = 0.05, μ/t = ?5.5 and Δ/t = 1.5, we find four peaks both for the diagonal, A(n(π/16, π/16), ω), the far left peak has a vanishing small weight; (b) in B(n(π/16, π/16), ω) the far left and far right peaks have very small weights. The physical picture is, then, that the pair physics in the normal phase (T > T _c is still valid below T _c . However, the condensation of the e-h pairs produces an additional gap around the chemical potential as in BCS, in other words, superconductivity opens a gap in the lower branch of a Hubbard-type-I solution.     

Cluster calculations of the hyperfine properties of copper compounds

Spin-polarized ab-initio cluster procedures are used to investigate the electronic structure of CuO₂-planes in the La₂CuO₄ and YBa₂Cu₃O₇ compounds. In particular, electric field gradients (EFGs) and magnetic hyperfine interaction parameters for the Cu sites were calculated with various theoretical methods. Calculations with density functional theory reproduce the experimentally determined EFGs fairly well while those at the Hartree-Fock level generally yield values which are too large by about 40%. The anisotropic magnetic hyperfine coupling can also be calculated with reasonable accuracy. This revised version was published online in August 2006 with corrections to the Cover Date.     

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Ohne Zusammenfassung

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Book reviews

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Notices bibliographiques

     

Buchbesprechungen

Ohne Zusammenfassung

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Book reviews

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Notices bibliographiques

     

Superconducting properties of the attractive Hubbard model

A self-consistent set of equations for the one-electron self-energy in the ladder approximation is derived for the attractive Hubbard model in the superconducting state. The equations provide an extension of a T-matrix formalism recently used to study the effect of electron correlations on normal-state properties. An approximation to the set of equations is solved numerically in the intermediate coupling regime, and the one-particle spectral functions are found to have four peaks. This feature is traced back to a peak in the self-energy, which is related to the formation of real-space bound states. For comparison we extend the moment approach to the superconducting state and discuss the crossover from the weak (BCS) to the intermediate coupling regime from the perspective of single-particle spectral densities.