Development of time-dependent second-principles simulations to study the transport and optical properties of materials
ABSTRACT: One of the most important properties of matter is its response to the application of external electric fields. The control of this phenomenon is is behind much of the current technology. A microscopic understanding of the mechanisms behind charge transport started with Drude at the beginni...
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| Tipo de recurso: | tesis de maestría |
| Fecha de publicación: | 2021 |
| País: | España |
| Institución: | Universidad de Cantabria (UC) |
| Repositorio: | UCrea Repositorio Abierto de la Universidad de Cantabria |
| Idioma: | inglés |
| OAI Identifier: | oai:repositorio.unican.es:10902/25154 |
| Acceso en línea: | http://hdl.handle.net/10902/25154 |
| Access Level: | acceso abierto |
| Palabra clave: | Charge transport Second principles model Localization Wannier functions Band disentanglement Fatbands Orbital character Transporte de carga Modelo de segundos principios Localización Funciones de Wannier Desentrelazamiento de bandas Carácter orbital |
| Sumario: | ABSTRACT: One of the most important properties of matter is its response to the application of external electric fields. The control of this phenomenon is is behind much of the current technology. A microscopic understanding of the mechanisms behind charge transport started with Drude at the beginning of the XX century who created an empirical model that is still widely used today, continued with the semiclassical theory of transport in the 30s that added a quantum-mechanical description to the movement of electrons in a material, and is currently an open line of research focused in graphene and other systems that display non-trivial topological band structures. In the last decades the advances in computation, using first principles methods such as density functional theory (dft), have allowed improving our understanding of the electronic structure of materials. However, the ability to study transport using these methods, as well as the effects of temperature is still very limited. In recent years a new family of techniques based on dft, known as second principles (sp), have been developed to solve these difficulties. Its practical application requires the construction of models (extension of tight binding models including one electron, electron-electron and electron-phonon interactions), written in a basis set of localized functions: The Wannier basis set. However, as introduced by Kohn in the 60s, the ground state of metallic systems (main conductors of the electric current) are characterized by a wavefunction highly delocalized, so the use of localized functions like Wannier orbitals for their description seems contraindicated. To further complicate the problem, bands in metals are strongly entangled and it will be necessary to isolate the key bands that describe the behaviour of the system around the Fermi energy. In this work we perform a computational study of elemental metallic and semiconducting struc tures. We analyze the wannierization problem of these systems. We try to study the chemical origin of their bands (orbital character) by the calculation of the fatbands associated to the Wan nier orbitals, in order to gain intuition that helps in model generation. Besides, we present a brief introduction in theory of transport and localization of the ground state. As technical results, we collect the basics of first and second principles, as well as the model generation program and the systematic procedure used for the calculation of the Wannier functions in this work. |
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