Computational design of nanostructured materials with renewable energy applications

Resumen

This thesis studies the viability of various materials as key pieces in the construction of thermosolar power plants as well as for the storage of solar energy. As these materials are exposed to extreme pressure and temperature cycles, it is important to study their behavior under these conditions. To do this, we have used different techniques with classical and quantum calculations at the molecular level. These calculations are essential to understand the structural behavior of materials as well as to design and predict the behavior of new materials. The purpose of the thesis is divided into two parts clearly related to each other: (1) to develop new methods to fit force fields of relevant materials in the energy plan, starting from the electronic density computed with DFT and avoiding the numerical dependence of the parameters of the potentials, and (2) design new nanostructured materials that can improve energy efficiency overcoming the adverse weather conditions of solar thermal power plants, using, where possible, models of force fields improved with our new methodology. The thesis is divided into six chapters covering the following topics: Chapter 1. In this chapter we begin with a summary of the thesis and continue presenting each and every one of the methods and materials used. We also present the theoretical basis behind this study, specific and detailed methodology as well as hardware and software specifications used for all analyzes. Chapter 2. We developed a new method to fit the parameters of an interatomic potential for nickel-chromium alloys, improving the prediction of the structural properties of these materials. To do this, we have designed an algorithm that carries out a series of iterations, in which the parameters of an existing potential are fitted, in order to optimize them based on a series of experimental observables. As an application, we study different structural properties of alloys with different concentrations of nickel-chromium, as well as nanoparticles of different sizes using the developed potential. We include at the end an example of the possible sintering of pairs of nanoparticles of this material. Chapter 3. We improve the fitting method developed in Chapter 2 and the prediction of the properties of metallic alloys. The improvement resides in the quantum study of the electron density of these materials, from which we fit the parameters of the classical potentials corresponding to said density. The use of ab-initio observables represents a qualitative advance, since obtaining the force fields is not subject to the value of the experimental observables. In addition, we expanded the composition of the metallic alloys studied by adding iron and molybdenum to the model, with the intention of getting as close as possible to the composition of INCONEL 625. Chapter 4. This chapter is the first of two focused on the search for new energetic materials. We have proposed, from a theoretical point of view, a new ordered nanoporous metal using as a model Metal-Organic Frameworks (MOFs), MOFs with modified ligands, zeolites and cristobalites, substituting SiO4 tetrahedra for supertetrahedra. The process is simple, using a program written in FORTRAN, we have filled the pores of these materials with metal and we have removed the original structure. We have performed 100 nanosecond molecular dynamics at different temperatures to verify that the ordered nanoporous metals are stable. For these simulations, we have used some force fields from the literature in addition to those developed by us in the previous chapters. The predictive power of this study is useful from an experimental point of view, since it relates the limiting diameter of the pores as a function of the stability of the new materials. The diffusion of relevant molecules in various fields such as water and xylene is studied as an application of these materials. Chapter 5. We continue with the creation of new materials presenting one composed of cubic silicon carbide nanoparticles in an amorphous silicon matrix, as an alternative to metallic alloys, due to the high resistance of this type of ceramics to temperature changes. To do this, we have studied simple structures of cubic, hexagonal and amorphous silicon carbide with a series of potentials to determine which of them best models the structural properties compared to existing experiments. Once this was done, we studied two composite materials, (1) flat interfaces of cubic silicon carbide versus amorphous silicon and (2) nanoparticles arranged within matrices of amorphous silicon. We have studied both types with different sizes to observe their behavior based on their densities. This study was complemented on the microscopic and macroscopic scale. On the first one, the mechanical properties of these materials were studied by performing microstructural lattice simulations. On the second one, to complete the upscaling approach, we have created ceramic tubes for receivers of thermo-solar power plants, seeing their temperature distribution based on their thickness. Chapter 6. We discuss the conclusions of the study carried out and focus on the directions this work could take in the future.