The search for good theoretical descriptions of the electronic structure and related physical properties of narrow band materials started at least 50 years ago and is still the primary occupation of a large group of chemists and physicists. Although a lot of progress has been made one must admit that we are still far removed from a general theoretical description of narrow band materials. Rather than being able to predict heavy fermion behaviour in say UPt3 or superconductivity in non-stoichiometric oxides, the theoretical community is continually caught off guard by such experimental discoveries. Although “predictions” after the fact are quite common and often successful, the situation of the high Tc materials seems to be a lot different. As Falicov states at this workshop “there are now N theories for high Tc materials (N ≃ 20) of which at least N-1 are not applicable”.
KeywordsCharge Fluctuation Heavy Fermion System Charge Transfer Energy Related Physical Property Heavy Fermion Behaviour
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