Investigação da transição isolante-metal do CDM via algoritmos computacionais e estudo de nano-dispositivos orgânicos

Abstract

We present in this work a theoretical study on conjugated organic polymers. These systems, in general semiconductors or insulators, when doped, show an increase in electrical conductivity. Under action of electric field, small oligomers can present a similar behavior to of usual devices, but with innumerable advantages as, for example, size extremely reduced (some nanometers). In the first chapter we will make a brief introduction on organic polymers conjugated showing some experimental results for 4-dicianometileno-4,4-ciclopenta polymer [2,1-b: 3,4b'] ditiofeno - CDM, that is the central object of study. Chapter 2 deals with the used quantum methods. We will cite the Hartre-Fock (HF) approximation and its semiempirical derivations. The Configuration Interaction (CI) method and the Density Functional Theory (DFT) also will be treated in this chapter. Chapter 3 is dedicated to describe the characteristics of some usual devices as diodes and transistors. We will still cite some extremely small electronic devices. Chapter 4 describes our results and quarrels about the possibility the of the transistion insulator-metal in CDM when doped. We got the characterization optics of oligomers of CDM with null charge and in the presence of defects of the type bipolaron. From the Hartree-Fock level we calculate the Structure of Bands and the Density of States (DOS) for the PCDM in the neutral and doped state. The calculation of the DOS and the Dispersion had been carried through computational programs developed here in the Group GFMA. We still present in this chapter the theoretical absorption spectra for oligomers of CDM with geometry fully optimized by DFT. In chapter 5 we have the relative results to the analysis of nanodevice based on tetramers of CDM with and without charge. The curves of the charge displacement versus voltage present characteristics of curves of usual devices. We also analyze the theoretical absorption spectra of the nanodevice for values of null tension and in points of current saturation.