Propiedades electrónicas en Nanotubos: un Estudio Ab Initio
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Morales Ochoa, Keiler Elionarka
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Trabajo de grado - Maestría
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EspañolFecha de publicación
2017-06
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Comprender el comportamiento de sistemas mesoscópicos, como son los nanotubos de carbono, en términos de sus propiedades electrónicas contribuye a establecer más y mejores criterios, que pueden aportar a la evaluación de materias primas, dada la necesidad de mejorar los recursos y ser responsables en la utilización de los mismos. Desde su descubrimiento los nanotubos de carbono de pared simple, se han generado grandes expectativas por sus potenciales usos. De otra parte, implementaciones del formalismo de la Teoría del Funcional de la Densidad (DFT) son herramientas ampliamente usadas para el análisis teórico de sistemas de dimensiones reducidas, una de ellas es el código SIESTA y el cual es usado en el presente estudio. Usando pseudopotenciales que conservan la norma y funcionales de correlación e intercambio en la Aproximación de Gradiente Generalizado, GGA , se calcula la energía de cohesión y propiedades electrónicas como la estructura de bandas, la densidad de estados y la densidad de carga electrónica para nanotubos de diferentes quiralidades. Los resultados son similares a lo establecido por la ley de Hamada para nanotubos con diámetro superior a los 0.4 nm. Estos resultados son equivalentes a los encontrados por el método de enlace fuerte o Tight Binding. En nanotubos con diámetros inferiores los resultados encontrados mediante DFT contrastan fuertemente con los de métodos empíricos donde los efectos de la hibridación de los orbitales debido a la curvatura son despreciados.
Abstract. Understanding the behavior of mesoscopic systems, such as carbon nanotubes, in terms of their electronic properties helps to establish more and better criteria, which can contribute to the evaluation of raw materials, given the need to improve resources and be responsible in the use of them. Since its discovery, single wall carbon nanotubes, SWCN, have generated great expectations for their potential uses. On the other hand, implementations of the formalism of the Density Functional Theory (DFT) are widely used tools for the theoretical analysis of systems of reduced dimensions, one of them is the SIESTA code and which is used in the present study. Using pseudopotentials that conserve the standard and functional correlation and exchange in the Generalized Gradient Approach, GGA, the cohesion energy and electronic properties are calculated as the band structure, the density of states and the electronic charge density for nanotubes of different chiralities. The results are similar to that established by Hamada's law for nanotubes with a diameter greater than 0.4 nm. These results are equivalent to those found by the strong bond or Tight Binding method. In nanotubes with lower diameters the results found by DFT contrast strongly with those of empirical methods where the effects of the hybridization of the orbitals due to the curvature are neglected.
Abstract. Understanding the behavior of mesoscopic systems, such as carbon nanotubes, in terms of their electronic properties helps to establish more and better criteria, which can contribute to the evaluation of raw materials, given the need to improve resources and be responsible in the use of them. Since its discovery, single wall carbon nanotubes, SWCN, have generated great expectations for their potential uses. On the other hand, implementations of the formalism of the Density Functional Theory (DFT) are widely used tools for the theoretical analysis of systems of reduced dimensions, one of them is the SIESTA code and which is used in the present study. Using pseudopotentials that conserve the standard and functional correlation and exchange in the Generalized Gradient Approach, GGA, the cohesion energy and electronic properties are calculated as the band structure, the density of states and the electronic charge density for nanotubes of different chiralities. The results are similar to that established by Hamada's law for nanotubes with a diameter greater than 0.4 nm. These results are equivalent to those found by the strong bond or Tight Binding method. In nanotubes with lower diameters the results found by DFT contrast strongly with those of empirical methods where the effects of the hybridization of the orbitals due to the curvature are neglected.