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-Gouterman (FG) transformation which diagonalizes the excitonic subspace. The 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 further unitary transformations which aim at simulating the competing influences in the FG equations. It is found that the displaced antisqueezing type is a suitable description for the ground state in the low coupling 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.