En las fronteras de la Materia Condensada

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.