Papers by Angel morales garcia
Journal of Materials Chemistry A, 2022
A systematic density functional theory study to investigate the stability of single-atom catalyst... more A systematic density functional theory study to investigate the stability of single-atom catalysts (SACs) over a series of O-terminated MXenes with the stoichiometry of M2CO2.
Physical Chemistry Chemical Physics, 2021
Reliable core-level binding energies of B(1s) and N(1s) in B,N-doped graphenes based on ab initio... more Reliable core-level binding energies of B(1s) and N(1s) in B,N-doped graphenes based on ab initio quantum chemical calculations.
Physical Chemistry Chemical Physics, 2021
First-principles based on density functional theory (DFT) calculations were performed to investig... more First-principles based on density functional theory (DFT) calculations were performed to investigate the interaction of two-dimensional (2D) HfS2 with SO2, a harmful gas with implications for climate change.
Physical Chemistry Chemical Physics, 2020
A density functional theory-based study shows that surface energy stabilization reconstruction me... more A density functional theory-based study shows that surface energy stabilization reconstruction mechanisms of transition metal carbides and nitrides occur when featuring a crystal structure different from most stable polymorph, and driven by its instablity.
Physical Chemistry Chemical Physics, 2020
Excited state topological descriptors based on the attachment/detachment one-electron charge dens... more Excited state topological descriptors based on the attachment/detachment one-electron charge density are used to investigate the centroids of photoactive TiO2nanoclusters and nanoparticles.
Physical Chemistry Chemical Physics, 2019
Density functional theory simulations and ab initio kinetic phase diagrams reveal that the CO2 ca... more Density functional theory simulations and ab initio kinetic phase diagrams reveal that the CO2 capabilities of MXenes are barely affected by their width.
Physical Chemistry Chemical Physics, 2018
Suitable and practical way to estimateOgapof TiO2nanoparticles containing up to thousands of atom... more Suitable and practical way to estimateOgapof TiO2nanoparticles containing up to thousands of atoms from computationally affordable relativistic all-electron calculations with a numerical atomic centered orbital basis set.
Physical Review B, 2017
Twisted bilayer graphene (tBLG) represents a family of unique materials with optoelectronic prope... more Twisted bilayer graphene (tBLG) represents a family of unique materials with optoelectronic properties tuned by the rotation angle between the two layers. The presented work shows an additional way of tweaking the electronic structure of tBLG: by modifying the interlayer 2 distance, for example by a small uniaxial out-of-plane compression. We have focused on the optical transition energy, which shows a clear dependence on the interlayer distance, both experimentally and theoretically.
Introducción. 1 Polimorfos de SiO 2 y CO 2. Analogías a altas presiones. 3 Motivación y Objetivos... more Introducción. 1 Polimorfos de SiO 2 y CO 2. Analogías a altas presiones. 3 Motivación y Objetivos de la Tesis Doctoral. 6 Organización de la Memoria. 7 Referencias 10 2 2.1 Formalismos Teóricos y Computacionales. 13 Estructura electrónica en sólidos cristalinos. 14 2.1.1 Teoría del Funcional de la Densidad. 15 2.1.1.1 Aproximaciones al potencial de intercambio y correlación. 17 2.1.2 Condiciones de periodicidad. 20 2.1.2.1 Teorema de Bloch. 20 2.1.2.2 Conjunto de bases de ondas planas. 21 2.1.3 Pseudopotenciales. 22 2.1.4 Optimización geométrica. 24 2.2 Estabilidad dinámica. 25 2.2.1 Dinámica de redes y estructura electrónica. 26 2.2.2 Teoría de perturbación del funcional de la densidad. 30 2.3 Estabilidad estática. Ecuaciones de estado en sólidos. 33 2.3.1 Consideraciones experimentales. 33 2.3.2 Ecuaciones de estado analíticas. 34 2.3.2.1 Ecuación de Vinet. 35 2.3.2.2 Ecuación de Birch-Murnaghan. 36 2.3.3 Ajuste no lineal. 37 2.4 Termoquímica de reacciones de estado sólido. 38 2.4.1 Calor de la reacción química. 38 2.4.2 Ley de Hess. 40 2.5 Topología de la superficie de energía potencial. Búsqueda de estructuras. 41 2.5.1 Algoritmo evolutivo. 42 IV 2.5.1.1 Espacio de búsqueda, población y función de idoneidad. 44 2.5.1.2 Representación. 44 2.5.2 Optimización local y restricciones. 46 2.5.3 Primera generación. 46 2.5.4 Operadores variacionales. 48 2.5.5 Supervivencia y selección de los padres. 49 2.5.6 Halting criteria. 50 2.5.7 Convergencia prematura y cómo prevenirla: Función de descendencia. 52 2.5.8 Otras metodologías de búsqueda. 54 2.5.8.1 Simulated annealing. 54 2.5.8.2 Minima hopping 55 2.5.8.3 Metadinámica 56 2.6 Topología de la densidad electrónica y la función ELF. Enlace químico. 57 2.6.1 Topologia. 58 2.6.1.1 Sistemas dinámicos. 59 2.6.1.2 Puntos críticos del campo. 60 2.6.2 Topología de la densidad electrónica. 62 2.6.2.1 Características generales de ρ. 63 2.6.3 Teoría de átomos en moléculas: AIM. 63 2.6.3.1 AIM en sólidos. 66 2.6.4 Función de Localización Electrónica: ELF. 68 2.6.4.1 Definición original de la ELF. 68 2.6.4.2 ELF en los funcionales de la densidad. 70 2.6.4.3 Aplicación de ELF al estado sólido. 71 Referencias 73 3 3.1 Resultados. 77 DFT+U calculations of crystal lattice, electronic structure, and phase stability under pressure of TiO 2 polymorphs. 77 3.1.1 Sinopsis. 77 3.1.2 Introduction. 79 3.1.3 Methodology. 81 3.1.4 Results and Discussion. 82 3.1.4.1 Crystal structure. 82 3.1.4.2 Electronic structure of anatase and rutile. 84 3.1.4.3 Phase stability. 87 3.1.4.4 Transition pressures. 90 3.1.5 Conclusions. 90 3.2 Local properties in SiO 2 at high pressure. Topological analysis. 93 V
MRS Proceedings, 2015
ABSTRACTNa2Ti3O7, a potential negative electrode for Na batteries, is investigated by combining e... more ABSTRACTNa2Ti3O7, a potential negative electrode for Na batteries, is investigated by combining experiments and first-principles calculations at the Density Functional Theory (DFT) level. A structural model is proposed for the reduced phases (A2+xTi3O7), with all alkali ions in octahedral coordination, leading to a distorted rocksalt type structure. The calculated elastic constants support the mechanical stability of the proposed Na4Ti3O7 structure. Calculated average intercalation potentials are 0.37 V for Na insertion in Na2Ti3O7 and 1.46 V for Li insertion in Li2Ti3O7, being in very good agreement with the values observed experimentally (0.3 V and 1.6 V respectively). The higher polarizing character of Li ions vs Na ions acts as a key-factor to bring the Li intercalation voltage 0.7 V above that of Na intercalation in layered-A2Ti3O7 materials.
Nano Letters, 2015
Tuning the electronic structure of 2D materials is a very powerful asset toward tailoring their p... more Tuning the electronic structure of 2D materials is a very powerful asset toward tailoring their properties to suit the demands of future applications in optoelectronics. Strain engineering is one of the most promising methods in this regard. We demonstrate that even very small out-of-plane axial compression readily modifies the electronic structure of monolayer MoS 2. As we show through in situ resonant and nonresonant Raman spectroscopy and photoluminescence measurements combined with theoretical calculations, the transition from direct to indirect band gap semiconductor takes place at ∼0.5 GPa, and the transition to a semimetal occurs at stress smaller than 3 GPa.
Materials Research Express, 2015
ABSTRACT
We propose a microscopic mechanism that describes how the structure and bonding network of α-crit... more We propose a microscopic mechanism that describes how the structure and bonding network of α-critobalite transforms into stishovite at constant pressure and temperature. A martensitic-like approach that preserves the traslational symmetry is used to modelize the simultaneous and coordinated movement of all the atoms as the transition progresses. Relevant distances and angles, cell strains, and atomic displacements across the transition path are obtained from first-principles calculations under the generalized gradient approximation of the density functional theory. A soft and symmetric energetic profile is computed with an activation barrier lower than 100 kJ/mol at the thermodynamic transition presure. Thanks to the analysis of the calculated topology of the electron localization function, we are able to provide visual and quantitative information on the chemical bonding reorganization that accompanies this transformation, mainly the increasing of Si and O coordinations from 4-fold...
Theoretical Chemistry Accounts, 2014
ABSTRACT By means of the quantum theory of atoms in molecules (QTAIM), we carry out a microscopic... more ABSTRACT By means of the quantum theory of atoms in molecules (QTAIM), we carry out a microscopic analysis of the response to hydrostatic pressure (p) of α-quartz, coesite, stishovite, CaCl2-type, and α-PbO2-type polymorphs of silica (SiO2). According to QTAIM atomic charges, there is not a substantial change in the ionic character of the bonding network (often described as polar covalent) along the pressure- induced polymorphic sequence. Atomic volumes (Vi) reveal that Si atoms remain with similar values regardless the polymorph, whereas oxygen follows the same volume collapses as the unit cells upon phase transformations. The inert character of Si is also displayed when local pressures(pi = −dE/dVi , E is the energy per formula unit) are computed. We obtain linear trends (pSi = 9.40 p and pO = 2.22 p) with a greater slope in the case of Si, illustrating its greater resistance to reduce its volume as pressure is applied. QTAIM also allows the evaluation of the atomic contributions to the bulk compressibility. Interestingly enough, we found a change in the atom showing the lowest compressibility, which is silicon in low-pressure phases but oxygen for stishovite and post-stishovite polymorphs.
The Journal of Physical Chemistry C, 2014
The Journal of Physical Chemistry C, 2013
The interplay of structural, energetic, and chemical bonding features across the pressure-induced... more The interplay of structural, energetic, and chemical bonding features across the pressure-induced αcristobalite → stishovite phase transition in SiO 2 is fully characterized by first principles calculations and topological analysis of the electron localization function. Under a martensitic approach, the transition mechanism is theoretically modeled at the thermodynamic transition pressure using the α-cristobalite P4 1 2 1 2 space group. A soft and symmetric transition path is determined with an activation barrier lower than 100 kJ/mol. No bond breaking is found, but a synchronous bonding formation process leading to Si 6-fold and O 3-fold coordinations. Only when the third coordination sphere of oxygens approaches a given Si at a distance close to 2.0 Å do new Si−O bonding basins appear. This situation occurs at a transformation stage well beyond the maximum in the energetic profile of the transition path.
The Journal of Physical Chemistry A, 2014
Covellite (CuS) is an important mineral sulfide that can be used in many technological applicatio... more Covellite (CuS) is an important mineral sulfide that can be used in many technological applications. It has a simple formula but a complex structure consisting of alternating layers of planar CuS 3 triangles and CuS 4 tetrahedrons with S−S bonds. Accurate first-principles calculations are performed for covellite structure (CuS), aiming to provide insights about its structural, mechanical and electronic properties and to unveil the nature of its chemical bonding. DFT and DFT+U methods have been used and showed to be sensitive to the correlation treatment (U value). Although it is not possible to extract a universal value of the U, this study indicates that U = 5 eV is an adequate value. The electronic structure analysis shows a significant metallic character due to p(S)−d(Cu) orbital interactions up to Fermi level. The projected density of states indicates that most of the contribution comes from the atomic orbitals in the [001] plane of the covellite, explaining the conductivity anisotropy observed experimentally. Topological analysis of the electron density was performed by means of quantum theory of atoms in molecules (QTAIM). Two different topological charges in Cu and S were calculated, confirming an ionic model with mix-charges. This mineral presents ionic degree of ∼32%. On the basis of the QTAIM analysis, the covalent character of S−S bond is confirmed, and the favored cleavage of CuS at the [001] surface might be at the Cu−S bond. The S atoms occupy most of the cell volume, and their contributions dominate the crystal compressibility: κ(S) ≈ κ(CuS).
The Journal of Chemical Physics, 2011
This work investigates crystal lattice, electronic structure, relative stability, and high pressu... more This work investigates crystal lattice, electronic structure, relative stability, and high pressure behavior of TiO2 polymorphs (anatase, rutile, and columbite) using the density functional theory (DFT) improved by an on-site Coulomb self-interaction potential (DFT+U). For the latter the effect of the U parameter value (0 < U < 10 eV) is analyzed within the local density approximation (LDA+U) and the generalized gradient approximation (GGA+U). Results are compared to those of conventional DFT and Heyd-Scuseria-Ernzehorf screened hybrid functional (HSE06). For the investigation of the individual polymorphs (crystal and electronic structures), the GGA+U/LDA+U method and the HSE06 functional are in better agreement with experiments compared to the conventional GGA or LDA. Within the DFT+U the reproduction of the experimental band-gap of rutile/anatase is achieved with a U value of 10/8 eV, whereas a better description of the crystal and electronic structures is obtained for U <...
Inorganic Chemistry, 2013
The structural behavior of mineral Stromeyerite, AgCuS, has been studied by means of angle-disper... more The structural behavior of mineral Stromeyerite, AgCuS, has been studied by means of angle-dispersive X-ray diffraction measurements up to 13 GPa and ab initio total-energy calculations. Two high-pressure phase transitions are found at 1.4 and 5.7 GPa, from the initial distorted Ni 2 In-type phase (AuRbS-type, RP, space group Cmc2 1) through an anti-PbClF-type phase (HP1, space group P4/nmm) to a monoclinic distortion of this latter phase (HP2, space group P2 1 /m). The collapse of the metal− metal interatomic distances at the RP−HP1 transition suggests a stronger metallic behavior of the high-pressure phase. The compressibility of the lattice parameters and the equation of state of the first pressure-induced phase have been experimentally determined. First-principles calculations present an overall agreement with the experimental results in terms of the high-pressure sequence and provide chemical insight into the AgCuS behavior under hydrostatic pressure.
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Papers by Angel morales garcia