THE METAL-INSULATOR-TRANSITION IN POLYACETYLENE - VARIATIONAL STUDY OF THE PEIERLS-HUBBARD MODEL

The one-dimensional Peierls-Hubbard model is shown to describe in a na tural way the metal-insulator transition observed in polyacetylene as a function of doping. A single set of parameters is able to account fo r the insulating state at half filling (dimerization, optical gap), ch arged solitons close to half filling and a transition to a state with vanishing gap at a doping concentration of about 8%. A brief summary o f other scenarios relying on disorder and interchain coupling is also presented.