CHEMICAL GEMINAL CHARGE-TRANSFER, VIBRONIC DEGENERACY EFFECTS, AND DOPING EXCITONS IN SUPERCONDUCTIVITY

A quantum chemical view of charge transfer related to the Jahn-Teller effect involving two-electron functions (geminals) is compared with BC S theory, the Cooper pair, and Bipolaron theory. For different isotope effects, we have proposed a Renner-Teller mechanism for cyclic crysta ls (instead of linear molecules) and a Jahn-Teller effect for degenera te vibronic states (instead of degenerate electronic states alone). To illustrate examples of special doping structure in superconductors, w e consider (YBa2Cu3O7-0.25)(4) and (Nd2-0.125Ce0.125CuO4-0.625)(2 x 4) and employ exciton-like Covalon states to render an improved descript ion of the superconductive mechanism. (C) 1991 Academic Press.