THE HOLSTEIN-HUBBARD DIMER OF VARIABLE-LENGTH AS THE BUILDING-BLOCK OF THE CUO PLANE - ELECTRONIC AND PHONONIC TRANSITIONS

A polaronic Hamiltonian is obtained for a dimer of length a, including an Einstein phonon of frequency Omega, a Holstein coupling g(0), and all the electronic one-and two-body terms consistent with a single orb ital per site (the latter evaluated in terms of Wannier functions buil t from Gaussian atomic orbitals). Its ground state for given alpha, g( 0), and Omega is identified by independent and simultaneous optimizati on of the electronic and phononic parameters. As alpha varies, we find discontinuous changes of both electronic and phononic states, with in teresting physical implications.