EXACT NUMERICAL DIAGONALIZATION OF ONE-DIMENSIONAL INTERACTING ELECTRONS NON-ADIABATICALLY COUPLED TO PHONONS

We study the role of non-adiabatic Holstein electron-phonon coupling o n the neutral-ionic phase transition of charge transfer crystals which can be tuned from continuous to discontinuous, using exact numerical diagonalization. The variation of electronic properties through the tr ansition is smoothed by non-adiabaticity. Lattice properties are stron gly affected, and we observe both squeezing and antisqueezing, dependi ng on details of the adiabatic potentials, and identify the quantum un certainty of the phonons as the most sensitive measure of non-adiabati city. The adiabatic limit is regular for a continuous transition but t urns out completely inadequate near a discontinuous transition. The re levance of coherent-state approaches is assessed critically.