  We discuss a general approach to a realistic theory of the electronic
structure in materials containing correlated d- or f- electrons. The main
feature of this approach is the taking into account the energy dependence of
the electron self-energy with the momentum dependence being neglected (local
approximation). In the case of strong interactions (U/W>>1 - rare-earth system)
the Hubbard-I approach is the most suitable. Starting from an exact atomic
Green function with the constrained density matrix the band structure problem
is formulated as the functional problem on Nmm' for f-electrons and the
standard LDA-functional for delocalized electrons. In the case of moderate
correlations (U/W=1 metal-insulator regime) we start from the dynamical mean
field iterative perturbation scheme (IPS) of G. Kotliar et. al. and also make
use of our multiband atomic Green function. Finally for the weak interactions
(U/W<1 -transition metals) the self-consistent diagrammatic fluctuation-
exchange (FLEX)-approach of N. Bickers and D. Scalapino is generalized to the
realistic multiband case. We presents two-band, two-dimensional model
calculations for all three regimes. A realistic calculation in Hubbard-I scheme
with the exact solution of the on-site multielectron problem for f(d)- shells
was performed for mixed-valence 4f compound TmSe, and for the classical Mott
insulator NiO.
