A hybrid scheme for the electronic structure calculations of strongly correlated electron systems is proposed. The ab initio local density approximation calculation is used to construct the Wannier functions and obtain single electron and Coulomb parameters of the multiband Hubbard-type model. In strong correlation regime the electronic structure within multiband Hubbard model is calculated by the generalized tight-binding method, which combines the exact diagonalization of the model Hamiltonian for a small cluster ͑unit cell͒ with perturbation treatment of the intercluster hopping and interactions. For undoped La 2 CuO 4 and Nd 2 CuO 4 this scheme results in charge transfer insulators with correct values of gaps and dispersions of bands in agreement with the angle-resolved photoemission data.

Complex cobalt oxides known as cobaltites are reviewed, including LnCoO 3 -based perovskite-structured rare-earth cobaltites (where Ln is lanthanum or a lantha-nide), quasi-two-dimensional and quasi-one-dimensional cobaltites of the types LnCo 2 O 5d , La 2 CoO 4 , and Ca 3 Co 2 O 8 , and Na x CoO 2 Á yH 2 O superconducting compounds. Key experimental and theoretical results are presented, with emphasis on the interplay between charge, spin, and orbital degrees of freedom. Two problems of specific relevance to cobaltites Ð the spin state instability of Co 3 ions in LnCoO 3 , and the nature of superconductivity in Na x CoO 2 Á yH 2 O Ð are also given significant attention.

Fe K-edge x-ray magnetic circular dichroism of magnetite (Fe3O4) powders was measured with synchrotron radiation under variable pressure and temperature conditions in diamond anvil cell. The magnetic dichroism was observed to decrease discontinuously by approximately 50% between 12 and 16 GPa, independent of temperature. The magnetic transition is attributed to a high-spin to intermediate-spin transition of Fe2+ ions in the octahedral sites and could account for previously observed structural and electrical anomalies in magnetite at this pressure range. The interpretation of x-ray magnetic circular dichroism data is supported by x-ray emission spectroscopy and theoretical cluster calculations.