Dynamic Study Of Long-range Electronic Correlation In Polymers

In1977, the scientists discovered that conductivity of polyacetylene becomes largewhen it was doped. It becomes good conductor from insulator. From then on, peoplewere interested in the conducting polyacetylene. In studying the conducting polymers,people put forward new concepts such as solitons and fractional charges. Theconducting polymers are a sort of new materials which have a broad prospect ofapplications. The conducting polymers have good plasticity. The cost price to buy ischeap. It is convenient for mass production of them. At present, people have developeda variety of organic optoelectronic devices, such as light emitting diode (LED), fieldeffect transistor (FET), photovoltaic cells.With design of these devices, we are required to understand many microscopicprocesses, such as photochemical reaction, photo-excitation dynamics, andenergy-charge transport, which are in turn related to the dynamics of electron-latticecoupling in the conducting polymers. In this dissertation, we mainly study dynamicproperties of polaron in conductive polymer. In studying, we adopt the extended SSHmodel plus the long-range correlation Hamiltonian and natural boundary condition. Wecalculate changes of the long-range correlation energy with time in a finite length oftrans-polyacetylene under adiabatic condition in terms of dynamic method and effect ofthe long-rang electron correlation on polaron dynamics. It is found from ourcomputational results that the long-rang correlation first shows a non-periodic dampedoscillation with time when we add an electron or a hole into the trans-polyacetylenechain and then after some time the long-rang correlation energy goes to a constant valueand at the same time the stable lattice configuration of the system is formed. The timethat the long-rang correlation energy tends to a constant will be shorter with increasinglattice numbers.Chapter1is introduction to the structure of polyacetylene. Polymer chain isquasi-one-dimensional system; it has many new features, such as the Peierls instability,dimerization. We adopt Su-Schrieffer-Heeger model to describe the one-dimensionalsystem. Chapter2is about the elementary excitations in polymers. These elementaryexcitations include soliton, polaron, and bipolaron. We discuss charge distribution andenergy level structure in the elementary excitations. Chapter3is about the dynamicmodel and method. We discuss long-range electron correlation effect and the evolution of long-range electron correlation in time in different situations. At last, we discuss theapplication prospects of organic polymers.