EXCITON-INDUCED LATTICE-RELAXATION AND THE ELECTRONIC AND VIBRATIONAL-SPECTRA OF SILICON CLUSTERS

The geometrical structures and electronic and vibrational spectra of s ilicon clusters with 20, 60, and 70 atoms are investigated. Using a fi rst-principles quantum-molecular-dynamics method we obtain the equilib rium structures, and study the effects of an exciton-induced lattice r elaxation in these systems. The relaxation induced by the exciton may result in a strong distortion of metastable structures, accompanied by changes in the electronic and vibrational spectra. This photoinduced deformation is associated with the presence of nearly degenerate elect ronic states in the metastable structure, similar to spontaneous Jahn- Teller distortions. The distortion yields lower symmetry and energy, s uggesting the trapping of excitons in some of these structures.