Densidade espectral de estados de superfície

Orientador: Cylon Eudóxio Tricot Gonçalves da SilvaTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: Nós discutimos o método de matriz transferência para o cálculo da densidade espectral de estados eletrônicos de sólidos com planos de clivagens. O método é aplicado explicitamente a um modelo simples que apresenta hibridização s-d: um cristal cúbico simples com duas orbitais por átomo, uma derivada de uma banda estreita, tipo d, e a outra derivada de uma banda larga, tipo s. É analisado o efeito de relaxação sobre a criação de estados localizados de superfície. O método é aplicado a modelos realísticos paara o estudo da estrutura eletrônica dos metais de transição e seus compostos. Um cálculo da superfície ( 100 ) dos monóxidos de metais de transição ( TiO e VO ) revelam a existência de estados intrínsicos de superfície. É apresentado um estudo sistemático da superfície ( 100 ) do Fe nas fases paramagnética e ferromagnética. É analisada a importância da hibridização spd na existência dos estados de superfície. Através do formalismo de matriz transferência são discutidas as superfícies ( 100 ) e ( 110 ) do W. Os resultados obtidos para a superfície ( 100 ) estão em acordo com os dados obtidos em experimento de fotoemissão, permitindo entender-se a origem dos estados localizados de superfície. A densidade espectral de estados para a superfície ( 110 ) evidencia a existência de estados de superfície não obtidos por outros métodosAbstract: Not informed.DoutoradoFísicaDoutor em Ciência

Study Of Conformational Stability Of Polycarbonitrile-polyazine Copolymers

In a previous study we showed that the trans-polycarbonitrile polymer presents a strong deviation from the planarity suggesting that this conformation does not correspond to the most stable structure of the system. These non-planarity can affect significantly the electronic properties of the polymer. On the other hand the polyazine derivative, a conjugated polymer, a nitrogen containing analog of the polyacetylene, that can be considered the head-to-head polymer of the imine repeat unit, is a planar conjugated system with very small sigma-pi interaction. In this work we report a comparative study of the electronic structures and the electrical conduction properties of the polycarbonitrile-polyazine copolymers. Our results indicate that the planarity of the copolymers depends on the competition among carbonitrile-azine segments size and can lead to a conductive system.1021-31222122

Effect of bipolaron type of defect on the polyacetylene- polycarbonitrile copolyme

2 p. : il., tab.In the present work we report a theoreticaI study on the effect of the presence of corformational defects like bipolaron on the electronic properties of polyacetylene-polycarbonitrile copolymers. Negative Factor Counting and inverse interaction techniques have been used to evaluate densities of states and wave functions, respectively.. Our results show a finite density of state at the Fermi energy for high concentration defect. This fact, together with the extention of the highest occupied molecular orbital (HOMO) state, indicate the possibility to have the copolymer in the metallic regime

Policabornitrile: a semiemperical ab initio and de density functional study of molecular stability

2 p. : il., tabThe theoretical literature data with respectt o the electronic properties of this compound is quite scarce and makes use of the planar alltransStructure as the most stable for the calculations In this work semiempirical (AM1 and PM3), ab initio (at the Hartree-Fock level)and density functional theory (using the correlation functional of Vosko, Wilk and Nussair) were used to anaIyse the conformationalstability of the all-trans and all-cis dimers, t rimers and tetramers of polycarbonitrile.The semiempirical and ab initio calculations at theHartree-Fock level showed in general that the all-trans structure with respect to other conformers is the most unstable s tructure. TheInclusion of electronic correlation energy through t he MP2 calculations or the VWN functional method suggest that the trans structure isthe most stable. The relative energies calculated at the correlated level presented diferences around 2 kcal/mol among the differentconformers . While the all-cis compounds presented a planar structure for any of the three methods the all-trans polymer showed a strongdeviation of planarity with a set of local minima in its energy surface.These results suggestth that further calculations on the electronic properties of this polymer can be significantly different of those actually available in the literature

Electronic structure of polyacetylene with bonded oxygen

In this work we have studied the electronic structure of finite polyacetylene chains with structural oxygen-bonding models following data from 13C-NMR experiments. We have used a combination of Austin Method One and Hydrogenic Atoms in Molecules version 3 methods to perform geometric and spectroscopic calculations. Our results show that the electronically-active states are generally unaffected by the incorporation of oxygen. © 1992

Study of copolymer composed by polyacetylene and Polyazine

2 p. : il., tab.The polyacetylene was investigated by us showing the presence of conductive states in the Fermi level caused by a disordered distributionof defects of soliton type. Also we have shown that the polyazine polymer presentes conductive characteristics through defects of the bipolaron type for orderly and disordered systems. The aim of this investigation is to verify whether the copolymer from polyacetylene andpolyazine can be found on the metallic regime.For the calculations of this system we used semiempirical methods for the optimization ofthe geometry.Our results indicate that, when we take of charge from the structure,the bipolaron type of defect is formed on the copolyme