The Effect Of Long-range Correlation On Polythiophene Polaron

Since the high conductivity of doped polyacetylene was found, people has strongstudy interest on the organic polymer. Organic polymer not only has metal andsemimetal properties, can be used as a conductor or semiconductor, but also is easy toprocess, at low cost, good compatibility with the substrate, etc. Therefore, Organicpolymer is widely used in light emitting and spin devices. In order to improve the workefficiency of these devices, it is necessary to correctly understand the transportmechanism of carriers in the conductive polymer. Conductive polymer carrier is notextended electronic or hole state, but the self-trapped state coupled by electronic (suchas soliton, polaron and bipolaron) with lattice. They have different charge-spinrelationship. Soliton, polaron and bipolaron theories explain the experimentalphenomena well, promote the development of organic semiconductor theory and theactual application, and become a research hotspot in recent years.The establishment of the organic polymer model is a process of continuousimprovement and further. W. P. Su, J. R. Schrieffer and A. J. Heeger established SSHmodel solved many problems of the degenerate ground-state cis-polyacetylene.Therefore, Brazovskii and Campbell bring in Symmetry broken item, establishedextended SSH model. Electronic interaction influences importantly in polaronconfiguration and band structure. Here, we adopt extended Hubbard model to describethe influence. At the same time, the electron correlation has important influence on theelectronic structure of the electronic system. To study the correlation energy, Hohenbergand Kohn established density functional theory, Kohn and Sham proposed local areadensity approximation (LDA).They make an important contribution on the calculationof correlation energy, but don’t calculate the correlation energy under long-rangecoulomb interaction. Zhao first derived the long-range correlation formula andlong-range electronic correlation hamilton, which is of great significance for the studyof electron correlation.In the first chapter, polythiophene (the object of study of this paper), for example,the present research status,functional characteristics and application prospect of organicpolymer have been summarized.In the second chapter, we introduce a theoretical model used to studyone-dimensional organic polymer-the extended SSH model, describe the Hubbard model with electron-electron interactions and long-range correlation Hamiltonian,derived theoretically the Hamiltonian of polythiophene and elaborate a kind ofnumerical calculation of organic polymer last.In the third chapter, we describe the hamiltonian of polythiophene andelectron-electron interactions respectively by using SSH model and the extendedHubbard model with long-range correlation, and then study polaron problem in thechain of polythiophene by using a self-consistent approach. We obtain effects ofelectron-electron interactions and long-range correlation on configuration and electriccharge density of polaron by calculating. It can be found that long-range correlationmakes polaron configuration smaller, makes region of polaron narrower, makesoscillation of the charge density weaker. In a word,effect of long-range correlation onelectron transport in polymer can not be ignored. We calculate the average long-rangecorrelation of electron polaron and hole polaron and find correlation energy of electronpolaron is higher than that of ground state, while hole polaron is lower than that ofground state.In the forth chapter, we discuss hamiltonian of polythiophene, research theinfluence of the parameters’ different values on polythiophene’s lattice configuration andcharge density.In the last chapter of this thesis, research work is made a summary for this article,and I list the main research results, and look into the follow-up work, list severalfeasible research plan.