Variational approach to exciton transport in molecular-crystals. J

The variational results for the free energy of an interacting exciton phonon system are used to derive expressions for the scattering rate and diffusion constant of an exciton in such a system. These expressions are applicable to both wide and narrow band cases, and includes the possibility of an abrupt transition from wide band (free) exciton to narrow band (localized) exciton. Some comments are made on the possibility of observing this transition by thermal modulation spectroscopy

On the relaxation of a twolevel system: Beyond the weakcoupling approximation On the relaxation of a two-level system: Beyond the weak-coupling approximation

The model of two nondegenerate quantum levels coupled linearly and off-diagonally to a bath of quantum mechanical harmonic oscillators studied previously by Laird, Budimir, and Skinner is re-examined. Interpretations are made for both the fourth order population relaxation and dephasing processes. Some of the methods used are applied to the standard spin-boson problem. The question of experimental detection of predicted phenomena is discussed. An approximate method, based on a canonical transformation of the original Hamiltonian is proposed to study the problem