Multipole Coulomb interactions with several electrons per crystal site : crystal and mean fields, symmetry lowering, and loss of magnetic moments
Faculty of Sciences. Physics
Physical review : B : condensed matter and materials physics. - Lancaster, Pa, 1998 - 2015
, p. 1-16
University of Antwerp
A review of the technique of multipole expansion of the Coulomb interaction for a few electrons is presented. The correlation effects described by this multireference approach are beyond the methods based on a single determinantal wave function (standard electron band structure calculation and molecular orbital method). Starting with the Coulomb law, we use the technique of multipole expansion to calculate the crystal electric field, mean field, and symmetry lowering for a number of many-electron configurations (f(3), sf(3), pf(3), and df(3)). We consider these configurations as very relevant for a model where three f electrons are localized and the fourth electron is delocalized and can be expanded locally in s-, p-, d-states in the spirit of the tight binding model. Prompted by the ideas of the double exchange, we study the intrasite multipole interaction, which couples localized electrons (f(3)) to delocalized ones on the same crystal site. We show that this interaction may be responsible for an effective loss of magnetic moments when a suitable symmetry lowering takes place. The present approach can be considered as a microscopic foundation of Kondo demagnetization when the loss of magnetic moments occurs together with a structural phase transition. The approach may be relevant for cerium and NpO2.