Solitons in the system of interacting Frenkel excitons

The possible formation of solitons in a Frenkel exciton system, with excito n-exciton interaction only, is studied taking into account the Pauli charac ter of exciton operators. This is realized by choosing the trial function o f the system in the of the spin coherent state for spin 1/2. Possible solut ions include both 'bright' and 'dark' solitons. Strict conditions for the e xistence and stability of particular types of soliton are formulated by imp osing limitations on the values of the system parameters and soliton veloci ty. The energy-momentum relation for both types of solution is obtained. It is concluded that neither kind of soliton can exist if the effective dynam ical interaction is a repulsive one. Recent references concerning 'bright' and 'dark' solitons are critically assessed.