Correlated electron behavior often involves a "localized state" and its interaction with the
neighboring localized states or itinerant states. The specification of such states is rarely made,
however, and the common viewpoint is that such states are more or less atomic-like.
We have begun calculating specified Wannier functions using a full potential, all-electron method
(WIEN). Unlike the specification of Vanderbilt and coworkers, who have advocated
maximally-localized Wannier functions, we calculate Wannier functions whose projection onto the
atomic state(s) of interest is maximal -- they may be said to be "maximally atomic" subject to the
hybridization of the atomic orbital(s) with other orbitals.
The characteristics and uses of such orbitals will be illustrated with their application to
understanding the magnetic coupling in the cuprate "brown phase" compound
La4Ba2Cu2O10
which is a ferromagnetic insulator, and its isostructural cousin
Nd4Ba2Cu2O10
which is, however, an antiferromagnetic insulator. Identification of the Wannier function with the Cu(2+)
s=1/2 spin-orbital allows the identification of important interatomic direct exchange couplings that
account for the different typse of magnetic ordering in these two systems.
Work done in collaboration with W. Ku, H. Rosner, and R. T. Scalettar.
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