EXCITON-PHONON GROUND-STATE IN THE FULTON-GOUTERMAN FRAMEWORK - CONTRAST OF ANTISQUEEZING AND REFLECTION IN Q-SPACE

A prototype exciton-phonon Hamiltonian is subjected to the Fulton-Gout erman (FG) transformation which diagonalizes the excitonic subspace. T he evolving FG equations elucidate most clearly the two counteracting tendencies inherent in the model: self-trapping and anti-self-trapping . TWO types of test functions for the FG ground state are devised by f urther unitary transformations which aim at simulating the competing i nfluences in the FG equations. It is found that the displaced antisque ezing type is a suitable description for the ground state in the low c oupling regime but it is inappropnate for the large coupling case. The displaced reflective type yields acceptable results for all coupling- transfer combinations. A nonunitary generated as well as the adiabatic trial wave function are also discussed.