https://uvadoc.uva.es/handle/10324/36327 2026-04-11T20:56:13Z https://uvadoc.uva.es/handle/10324/65809 Estudio de las propiedades estructurales y magnéticas de agregados atómicos de hierro oxidados 2021-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/65557 Estudio de las capacidades de adsorción de hidrógeno de nanoporos formados por paredes de BC3 dopado con Li. 2024-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/65487 Estudio de las propiedades estructurales y electrónicas en la nanopartícula Ni13@Ag42, y los cambios que éstas sufren bajo oxidación analizando el papel que juega la capa protectora de Ag. 2024-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/65485 Estudio de las primeras etapas de oxidación en nanoaleaciones de ZnMg ricas en Zn para explorar las razones por las cuales estos materiales son buenos anticorrosivos 2021-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/65431 Estudio del dopado de popgrafeno con Li y de la capacidad de almacenamiento de hidrógeno en dicha nanoestructura 2021-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/65171 Estudio teórico de las capacidades de adsorción de hidrógeno de nanoporos de borofeno decorados con átomos de Li 2021-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/63842 The disparity between the masses of the two components in a binary liquid system can lead to the appearance of a peculiar phenomenon named “fast sound,” which was identified for the first time in Li4Pb several decades ago and later observed in other Li based alloys. However, the exact characteristics and nature of this phenomenon and the reasons behind its appearance have not totally been identified yet. In this work, we analyze the longitudinal and transverse current correlation functions of UO2 , Li4Pb, and Li0.17Pb0.83 , as obtained from ab initio molecular dynamics simulations. We find that fast sound appears to occur in the two former systems but not in the latter. Additionally, we discuss some of the properties of the liquid mixtures that may be related to the appearance (or absence) of the phenomenon, such as the composition, the polyhedral structure of the melt, and the type of bonding in the system. 2023-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/63838 We report a study on the static and dynamic properties of several liquid 5d transition metals at thermodynamic conditions near their respective melting points. This is performed by resorting to ab initio molecular dynamics simulations in the framework of the density functional theory. Results are presented for the static structure fac- tors and pair distribution functions; moreover, the local short range order in the liquid metal is also analized. As for the dynamical properties, both single-particle and collective properties are evaluated. The dynamical struc- ture shows the propagating density fluctuations, and the respective dispersion relation is obtained. Results are also obtained for the longitudinal and transverse current spectral functions along with the associated disper- sion of collective excitations. For some metals, we found the existence of two branches of transverse collective excitations in the region around the main peak of the structure factor. Finally, several transport coefficients are also calculated. 2023-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/63666 Metal-Organic Frameworks (MOFs) are a significant and promising category of solid that have garnered substantial attention for their potential in storing hydrogen and methane. Grand Canonical Monte Carlo (GCMC) simulations of the usable hydrogen and methane storage capacities of five DUT MOFs (Dresden University of Technology), based on tritopic ligands and copper, have been carried out at room temperature and pressures between 0.5 and 35 MPa. These DUT MOFs exhibit high usable hydrogen and methane storage capacities, comparable or higher than the storage capacities of the best classical MOFs and the best Cu-based MOFs. The usable methane gravimetric storage capacities at 35 MPa and room temperature of these DUTs reach the Department of Energy (DOE) methane gravimetric target and their usable volumetric capacities are close to the DOE methane volumetric target. 2023-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/61287 Novel materials capable of storing hydrogen or/and methane at high gravimetric and volumetric densities are required for hydrogen vehicles to be widely employed as a clean alternative to fossil-based vehicles. Metal-Organic Frameworks (MOFs) are considered as promising candidates to achieve the Department Of Energy (DOE) targets for both, hydrogen and methane storage. Using Grand Canonical Monte Carlo (GCMC) simulations, the hydrogen and methane gravimetric and volumetric storage capacities of two recently synthesized Al-nia MOFs have been studied. Their storage capacities have been compared with the storage capacities of other Al-based MOFs and classical and well-known MOFs, such as IRMOF-5. The two novel Al-nia MOFs have shown high hydrogen and methane gravimetric and volumetric storage capacities at room temperature and moderate pressures, 25–35 MPa, comparable or higher than the storage capacities of classical and Al-based MOFs. 2023-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/60426 Hydrogen Fuel Cell Electric Vehicles (HFCEVs) and Natural Gas Vehicles (NGVs) are cleaner alternatives to present oil-based vehicles. The main problem of these technologies is the on-board storage. Metal-organic frameworks (MOFs) is one of the main groups of solid porous materials that can be used to store hydrogen or methane on-board these vehicles at room temperature and low or moderate pressures. The synthesis of these materials is usually expensive. Recently a group of eleven new BUT MOFs (BUT: Beijing University of Technology) has been synthesized using cheap organic precursors. Grand Canonical Monte Carlo simulations (GCMC) of the hydrogen and methane storage capacities and isosteric heats of these BUTs have been carried out and analyzed at 298.15 K and at pressures in the range 0.5–50 MPa. The correlations between the storage capacities and the porosity, the density, the pore size and the isosteric heat of the MOFs are analyzed. According to the simulations, three of the newly developed BUTs demonstrated high storage capacities for both hydrogen and methane. BUT-104 and 105 exhibited useable hydrogen volumetric and gravimetric capacities of approximately 0.023–0.027 kg/L and 4 wt % at 50 MPa. Additionally, they showcased useable methane volumetric and gravimetric capacities of 0.16–0.21 kg/L and 25 wt % at 25–35 MPa. Moreover, BUT-107 achieved the U.S. Department of Energy (DOE) hydrogen target for 2025, with a useable hydrogen gravimetric capacity of 5.5 wt % at 27 MPa. Furthermore, BUT-107 met the corresponding DOE methane targets, with useable methane volumetric and gravimetric capacities of 0.25 kg/L and 33.33 wt % at 50 MPa. 2023-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/53599 The static and dynamic properties of several bulk liquid 4d transition metals at thermodynamic conditions near their respective melting points have been evaluated by using ab-initio molecular dynamics simulations. The calculated static structure factors show an asymmetric second peak followed by a more or less marked shoulder which points to a sizeable amount of icosahedral local order. Special attention is devoted to the analysis of the obtained longitudinal and transverse current spectral functions and the corresponding dispersion of collective excitations. For some metals, we have found the existence of two branches of transverse collective excitations in the second pseudo-Brillouin zone. Finally, results are also reported for several transport coefficients. 2022-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/52208 Grand Canonical Monte Carlo, GCMC, simulations are used to study the gravimetric and volumetric hydrogen storage capacities of different carbon nanopores shapes: Slit-shaped, nanotubes and torusenes at room temperature, 298.15 K, and at pressures between 0.1 and 35 MPa, and for pore diameter or width between 4 and 15 Å. The influence of the pore shape or curvature on the storage capacities as a function of pressure, temperature and pore diameter is investigated and analyzed. A large curvature of the pores means, in general, an increase of the storage capacities of the pores. While torusenes and nanotubes have surfaces with more curvature than the slit-shaped planar pores, their capacities are lower than those of the slit-shaped pores, according to the present GCMC simulations. Torusene, a less studied carbon nanostructure, has two radii or curvatures, but their storage capacities are similar or lower than those of nanotubes, which have only one radius or curvature. The goal is to obtain qualitative and quantitative relationships between the structure of porous materials and the hydrogen storage capacities, in particular or especially the relationship between shape and width of the pores and the hydrogen storage capacities of carbon-based porous materials. 2022-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/49067 Several static and dynamic properties of the liquid Li-Pb alloy at diverse compositions, have been calcu-lated by means ofab initiomolecular dynamics simulation study. This alloy has attracted much attentionbecause of the finding of fast sound at the Li0:80Pb0:20composition and also the technological interest ofthe the eutectic composition, Li0:17Pb0:83, as a component of the blanket in fusion reactors.Results are reported for total static structure factors, which are compared with the available experi-mental data. An additional analysis of the structure allows the quantification of the heterocoordinatingtendencies in this alloy, which at the Li0:80Pb0:20composition are largest and lead to a Pb-centered poly-hedral structure, where, however, Li4Pb units are not present.Regarding the collective dynamics, the calculated partial dynamic structure factors exhibit side peaksindicative of propagating density fluctuations, including density fluctuation modes with phase velocitygreater than the hydrodynamic sound velocity. Also, the longitudinal and transverse dispersion relationshave been calculated and its different branches analysed. We find all the high frequency branches tobehave as optic-like modes, contrary to other interpretations in terms of an acoustic-like fast soundmode.Some transport coefficients such as self- and inter-diffusion coefficients, shear viscosities and adiabaticsound velocities, have also been calculated. Finally, the obtained results for the electronic density ofstates clearly indicate the metallic character of the liquid LixPb1 xalloy. 2021-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/49024 The accurate description of the potential energy landscape of moderate-sized nanoparticles is a formidable task, but of paramount importance if one aims to characterize, in a realistic way, their physical and chemical properties. We present here a Neural Network potential able to predict structures of pure and mixed nanoparticles with an error in energy and forces of the order of chemical accuracy as compared with the values provided by the theoretical method used in the training process, in our case the density functional theory. The neural network is integrated into a basin-hopping algorithm which dynamically feeds the training process. The main ingredients of the neural network algorithm as well as the protocol used for its implementation and training are detailed, with particular emphasis on those aspects that make it so efficient and transferable. As a first test, we have applied it to the determination of the global minimum structures of ZnMg nanoalloys with up to 52 atoms and stoichiometries corresponding to MgZn and MgZn, of special interest in the context of anticorrosive coatings. We present and discuss the structural properties, chemical order, stability and pertinent electronic indicators, and we extract some conclusions on fundamental aspects that may be at the roots of the good performance of ZnMg nanoalloys as protective coatings. Finally, we comment on the step forward that the presented machine learning approach constitutes, both in the fact that it allows to accurately explore the potential energy surface of systems that other methodologies can not, and that it opens new prospects for a variety of problems in Materials Science. 2021-01-01T00:00:00Z https://uvadoc.uva.es/handle/10324/42646 The hydrogen storage capacities of nanoporous carbons, simulated as graphene slit-shaped pores, have been calculated using simple theoretical methods that do not involve computationally expensive calculations. The theoretical methods calculate the storage of hydrogen molecules on a solid porous material by using the Equation Of State, EOS, of the hydrogen gas and the interaction potential energy of H2 with the surfaces of the pores of the material. Calculations have been carried out using the same interaction potential energy and empirical EOS. The interaction potential energy is obtained from calculations of H2 on graphene, using a DFT-based method that includes the dispersion interactions. The storage capacities have been calculated as a function of pressure in the range 0.1–25 MPa, of pore width in the range 4.7–20 Å and at 80.15 and 298.15 K. The storage capacities obtained with the methods are compared and the advantages and limitations of the methods are discussed, as well as the storage capacities predicted by the methods for wide pores. These simple theoretical methods are useful to design novel materials for hydrogen storage. 2020-01-01T00:00:00Z