Mejora de los modelos generalizados de segundos-principios en sistemas de estado sólido: avances en modelos electrónicos y acoplamiento electrón-red

• Autores: Nayara Carral Sainz
• Directores de la Tesis: Pablo García Fernández (codir. tes.), Francisco Javier Junquera Quintana (codir. tes.)
• Lectura: En la Universidad de Cantabria ( España ) en 2025
• Idioma: español
• Títulos paralelos:
  • Improvement of generalized second-principles models for solid-state systems: advances in electron models and electron-lattice coupling
• Tribunal Calificador de la Tesis: Philippe Ghosez (presid.), Pablo Aguado Puente (secret.), Oswaldo Dieguez López (voc.)
• Programa de doctorado: Programa de Doctorado en Química Teórica y Modelización Computacional/Theoretical Chemistry and Computational Modelling por la Universidad Autónoma de Madrid; la Universidad Complutense de Madrid; la Universidad de Barcelona; la Universidad de Cantabria; la Universidad de Extremadura; la Universidad de las Illes Balears; la Universidad de Murcia; la Universidad de Oviedo; la Universidad de Sevilla; la Universidad de Vigo; la Universidad del País Vasco/Euskal Herriko Unibertsitatea; la Universidad Jaume I de Castellón y la Universitat de València (Estudi General)
• Materias:
  • Física
    • Física del estado sólido
• Enlaces
  • Tesis en acceso abierto en:  TESEO  UCrea 
• Resumen
  • español

    En esta tesis se presenta una metodología sistemática y cuasi-automatizada para la generación de modelos electrónicos en el marco de la teoría del funcional de la densidad de segundos-principios. Este enfoque permite la construcción de modelos precisos y computacionalmente eficientes mediante la derivación de todos los parámetros necesarios a partir de cálculos de primeros-principios sobre un conjunto de entrenamiento cuidadosamente diseñado. El formalismo incluye Hamiltonianos a un electrón, acoplamiento electrón-red e interacciones electrón-electrón, lo que posibilita una modelización precisa de las respuestas estructurales y electrónicas para la simulación de fenómenos complejos como polarones y excitones. En este trabajo aplicamos la metodología desarrollada en SrTiO3 y LiF, materiales representativos de perovskitas de metales de transición y aislantes de amplio gap, respectivamente, validando la robustez del enfoque.

  • español

    In this thesis we present a systematic, quasi-automated methodology for generating electronic models in the framework of second-principles density functional theory (SPDFT). Second-principles electronic models employ an effective multiscale approach for treating the relevant electronic degrees of freedom. In this framework they are represented by a tight-binding model corrected by electron-electron interactions. The Hamiltonian matrix elements are expressed in a basis of Wannier functions which are obtained from the band manifolds of interest in the problem. As a result, the first objective of this thesis was to study the methodology for constructing a Wannier function basis, which provides an exact tight-binding representation of the Hamiltonian matrix elements. This involved a comprehensive examination of both the theoretical foundation and its computational implementation using WANNIER90.

    At this point, the main goal of this thesis has been focused on the development of the methodology to fit automatically the parameters involved in the second-principles model considering one-electron Hamiltonians and including properly the electron-lattice coupling and the electron-electron interaction, enabling accurate modeling of structural and electronic responses. The developed approach derives all necessary parameters from first-principles calculations on a carefully designed training set with the objective of maintaining a high level of accuracy and predictive power similar to that of first-principles methods. Notably, this methodology relies entirely on theoretical input, without incorporating any experimental data.

    This thesis places particular emphasis on the study and calculation of electron-lattice interaction parameters, aiming to clarify their physical meaning and establish reliable methods for their determination. Electron-vibration interaction plays a crucial role in the understanding of different solid-state properties such a as charge and energy transport in polarons or structural distortions as the Jahn-Teller effect. Alongside a comprehensive review of state-of-the-art approaches to vi bronic coupling within the framework of density functional theory, we present a detailed theoretical analysis that connects these methodologies with the electron-lattice parameters used in second-principles models. Special attention is given to recent developments, including finite-difference techniques, reciprocal-space formulations, and Wannier function-based approaches, which serve as a foundation for the accurate parametrization of second-principles models.

    Accordingly, the chosen procedure for obtaining the electron-lattice interaction parameters involved their direct evaluation using the finite-difference method. In contrast, the determination of electron-electron interaction parameters was carried out by fitting these parameters to first-principles calculations through the minimization of a suitably defined goal function. A key feature of our method is the enforcement of space group symmetries, which reduces both the number of independent parameters and the required computational effort.

    Finally, we apply the methodology to SrTiO3 and LiF, materials representative of transition-metal perovskites and wide-band-gap insulators, respectively. In both cases, the resulting models reproduce DFT reference data with high fidelity across various atomic configurations and charge states. Our results validate the robustness of the approach and highlight its potential for simulating complex phenomena such as polarons and excitons.