Enfoques computacionales en hidrato-clatratos: desde agregados moleculares de tamaño finito a sistemas de redes extendidas

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química. Fecha de Lectura: 17-11-2022Esta tesis tiene embargado el acceso al texto completo hasta el 17-05-2024This thesis is dedicated to the study of clathrate hydrate systems. The formation of these crystalline frameworks and their properties at specific thermodynamic conditions depend on the interactions between the trapped molecules and the water host lattice. Understanding their energy and structural stability allows controlling properties involved in different technological applications as a potential material in the fight against environmental problems related to the capture and storage of greenhouse gases. In this work, first-principles electronic structure methods are used to study clathrate-like cluster and periodic crystal systems of CO2@sI/sII/sH. The estimation of the underlying guest-host and host-host interactions, between the trapped molecules (guest) and the guest lattice (host) of water, dominated by hydrogen bonds and van der Waals forces, is fundamental in determining the properties and formation mechanisms for such structures, with their adequate description being a significant challenge. More specifically, the area of interaction transferable model development lacks reference data for aggregates to macro (bulk) systems. Thus, through first-principles electronic structure computational modeling reference data has been provided from clathrate-like cluster systems to periodic lattices of CO2@sI/sII/sH clathrates. In particular, a comparative evaluation (benchmarking) between traditional and modern density functionals of different families, and dispersion correction schemes together with data from high-level ab initio calculations is presented. In this way, high-quality reference data has been provided that contributes to the development of new data-driven models, trying to answer open questions and challenges in the field of GCS (gas-control storage) technologies. The CO2@sI clathrate hydrate, the most common observed, represents the first part of this work. Its stability is evaluated by combining bottom-up and top-down quantum chemistry approaches. The first approach proposes to study intermolecular interactions in finite-size systems of individual and specific arrangements of two-adjacent cages of the crystal lattice system. The second approach considers the unit cell that reproduces the periodic crystal and studies the effects of the lattice through a systematic evaluation of different density functionals. Methodologies such as linear scaling DFT for CO2@sI supercells are also explored while DLPNO methodologies are used for aperiodic systems. Guest/host interactions are also investigated by implementing semi-empirical potential and ab initio-based two body water-water, CO2-water interaction models, though a sum of potentials scheme is considered and compared with the DFT+D data. The second and third parts of this work are dedicated to the structures CO2@sII and CO2@sH respectively. Electronic structure calculations are presented to describe the energetics associated with gradual filling processes of the unit cells, the orientation of the CO2 within the individual cages and the crystal lattice, as well as the effects of pressure on structural parameters. Moreover, a study of multiple occupancy of CO2 molecules within the individual cages and unit cells of the three CO2@sI/sII/sH systems is also investigated and discussed, in terms of CO2 storage efficiency in such materialsEste trabajo de tesis ha sido posible gracias al programa de doctorado en Química Teórica y Modelización Computacional de la Universidad Autónoma de Madrid. A la financiación de MINECO, proyectos FIS2017-83157-P y PID2020-114654GB-I00 y los proyectos IND2017/AMB-7696 y IND2018 de la Comunidad de Madrid. Agradecer también a la fundación Santander por la beca recibida para la realización de una estancia de investigación. Así mismo, agradezco a los centros de computación del SGAI-CSIC y CESGA por el tiempo de cálculo en cluster al que tuve acces