 |
Center for Nonlinear Studies |
We outline the relevant history of DFT and the tight-binding realization of it, with application to polarons in the transition-metal oxides and perovskites. It is seen how the formation of a small polaron requires a localization energy, which must be less than the gain from lattice relaxation, both obtained explicitly in the theory. This replaces the traditional criterion of relaxation energy being greater than optical-mode phonon energy. It is seen to rule out small polarons in the dioxides of titanium, zirconium, and hafnium, but not the monoxide of manganese. A coupling between neighboring metallic sites, exactly that responsible for Heisenberg exchange in antiferromagnets, is a central quantity, obtained explicitly. It leads to delocalized polarons, if no single-site polaron is allowed, but for the systems considered always so delocalized that they simply raise the effective mass of the corresponding electrons slightly.
Host: John Wills