A model of localization,soliton propagation,and self-trapping in an electronically excited atomic lattice

The localization and propagation of electronic excitation is studied in a one-dimensional lattice of atoms, in which the interatomic potential is of Lennard-Jones (9-6) form. The dynamics are followed taking account of the full potential, bringing out aspects that do not appear in the harmonic approximation. Calculations are made first in a continuum model, and tested numerically for real systems. Electronic excitation of an atom may cause a change in its dispersive binding to neighbours, and there can be resonance coupling leading to excitation transfer and delocalization. With resonance coupling only, i.e. with no change in the dispersion interaction, the new result is found that there can be localization into states below the exciton band, arising from the changes in the strength of resonance coupling caused by variations in lattice spacing. These states become deeper when a change in dispersion energy is added; they can propagate as solitons without energy loss when the dispersion energy change is small; for larger changes the excitation is trapped.