12 results on '"Pérez-Osorio, Miguel A."'
Search Results
2. Bulk O2 formation and Mg displacement explain O-redox in Na0.67Mn0.72Mg0.28O2
- Author
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Boivin, Edouard, House, Robert A., Pérez-Osorio, Miguel A., Marie, John-Joseph, Maitra, Urmimala, Rees, Gregory J., and Bruce, Peter G.
- Published
- 2021
- Full Text
- View/download PDF
3. Superstructure control of first-cycle voltage hysteresis in oxygen-redox cathodes
- Author
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House, Robert A., Maitra, Urmimala, Pérez-Osorio, Miguel A., Lozano, Juan G., Jin, Liyu, Somerville, James W., and Duda, Laurent C.
- Subjects
Hysteresis -- Control ,Oxygen -- Electric properties -- Chemical properties ,Cathodes -- Electric properties ,Environmental issues ,Science and technology ,Zoology and wildlife conservation - Abstract
In conventional intercalation cathodes, alkali metal ions can move in and out of a layered material with the charge being compensated for by reversible reduction and oxidation of the transition metal ions. If the cathode material used in a lithium-ion or sodium-ion battery is alkali-rich, this can increase the battery's energy density by storing charge on the oxide and the transition metal ions, rather than on the transition metal alone.sup.1-10. There is a high voltage associated with oxidation of O.sup.2- during the first charge, but this is not recovered on discharge, resulting in reduced energy density.sup.11. Displacement of transition metal ions into the alkali metal layers has been proposed to explain the first-cycle voltage loss (hysteresis).sup.9,12-16. By comparing two closely related intercalation cathodes, Na.sub.0.75[Li.sub.0.25Mn.sub.0.75]O.sub.2 and Na.sub.0.6[Li.sub.0.2Mn.sub.0.8]O.sub.2, here we show that the first-cycle voltage hysteresis is determined by the superstructure in the cathode, specifically the local ordering of lithium and transition metal ions in the transition metal layers. The honeycomb superstructure of Na.sub.0.75[Li.sub.0.25Mn.sub.0.75]O.sub.2, present in almost all oxygen-redox compounds, is lost on charging, driven in part by formation of molecular O.sub.2 inside the solid. The O.sub.2 molecules are cleaved on discharge, reforming O.sup.2-, but the manganese ions have migrated within the plane, changing the coordination around O.sup.2- and lowering the voltage on discharge. The ribbon superstructure in Na.sub.0.6[Li.sub.0.2Mn.sub.0.8]O.sub.2 inhibits manganese disorder and hence O.sub.2 formation, suppressing hysteresis and promoting stable electron holes on O.sup.2- that are revealed by X-ray absorption spectroscopy. The results show that voltage hysteresis can be avoided in oxygen-redox cathodes by forming materials with a ribbon superstructure in the transition metal layers that suppresses migration of the transition metal. In oxygen-redox intercalation cathodes, voltage hysteresis can be avoided by forming cathode materials with a 'ribbon' superstructure in the transition metal layers that suppresses transition metal migration., Author(s): Robert A. House [sup.1] , Urmimala Maitra [sup.1] , Miguel A. Pérez-Osorio [sup.1] , Juan G. Lozano [sup.1] [sup.2] , Liyu Jin [sup.1] , James W. Somerville [sup.1] , [...]
- Published
- 2020
- Full Text
- View/download PDF
4. Dielectric screening in extended systems using the self-consistent Sternheimer equation and localized basis sets
- Author
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Hübener, Hannes, Pérez-Osorio, Miguel A., Ordejón, Pablo, and Giustino, Feliciano
- Subjects
Condensed Matter - Materials Science - Abstract
We develop a first-principles computational method for investigating the dielectric screening in extended systems using the self-consistent Sternheimer equation and localized non-orthogonal basis sets. Our approach does not require the explicit calculation of unoccupied electronic states, only uses two-center integrals, and has a theoretical scaling of order O(N^3). We demonstrate this method by comparing our calculations for silicon, germanium, diamond, and LiCl with reference planewaves calculations. We show that accuracy comparable to planewaves calculations can be achieved via a systematic optimization of the basis set., Comment: 6 pages, 3 figures
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- 2012
- Full Text
- View/download PDF
5. Performance of local orbital basis sets in the self-consistent Sternheimer method for dielectric matrices of extended systems
- Author
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Hübener, Hannes, Pérez-Osorio, Miguel A., Ordejón, Pablo, and Giustino, Feliciano
- Subjects
Condensed Matter - Materials Science - Abstract
We present a systematic study of the performance of numerical pseudo-atomic orbital basis sets in the calculation of dielectric matrices of extended systems using the self-consistent Sternheimer approach of [F. Giustino et al., Phys. Rev. B 81 (11), 115105 (2010)]. In order to cover a range of systems, from more insulating to more metallic character, we discuss results for the three semiconductors diamond, silicon, and germanium. Dielectric matrices calculated using our method fall within 1-3% of reference planewaves calculations, demonstrating that this method is promising. We find that polarization orbitals are critical for achieving good agreement with planewaves calculations, and that only a few additional \zeta 's are required for obtaining converged results, provided the split norm is properly optimized. Our present work establishes the validity of local orbital basis sets and the self-consistent Sternheimer approach for the calculation of dielectric matrices in extended systems, and prepares the ground for future studies of electronic excitations using these methods., Comment: 10 pages, 8 figures
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- 2012
- Full Text
- View/download PDF
6. Superstructure control of first-cycle voltage hysteresis in oxygen-redox cathodes
- Author
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House, Robert A., primary, Maitra, Urmimala, additional, Pérez-Osorio, Miguel A., additional, Lozano, Juan G., additional, Jin, Liyu, additional, Somerville, James W., additional, Duda, Laurent C., additional, Nag, Abhishek, additional, Walters, Andrew, additional, Zhou, Ke-Jin, additional, Roberts, Matthew R., additional, and Bruce, Peter G., additional
- Published
- 2019
- Full Text
- View/download PDF
7. Oxygen redox chemistry without excess alkali-metal ions in Na2/3[Mg0.28Mn0.72]O2
- Author
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Maitra, Urmimala, House, Robert, Somerville, James, Tapia-Ruiz, Nuria, Lozano, Juan, Guerrini, Niccoló, Hao, Rong, Luo, Kun, Jin, Liyu, Pérez-Osorio, Miguel, Massel, Felix, Pickup, David, Ramos, Silvia, Lu, Xingye, McNally, Daniel, Chadwick, Alan, Giustino, Feliciano, Schmitt, Thorsten, Duda, Laurent, Roberts, Matthew, Bruce, Peter, Maitra, Urmimala, House, Robert, Somerville, James, Tapia-Ruiz, Nuria, Lozano, Juan, Guerrini, Niccoló, Hao, Rong, Luo, Kun, Jin, Liyu, Pérez-Osorio, Miguel, Massel, Felix, Pickup, David, Ramos, Silvia, Lu, Xingye, McNally, Daniel, Chadwick, Alan, Giustino, Feliciano, Schmitt, Thorsten, Duda, Laurent, Roberts, Matthew, and Bruce, Peter
- Abstract
The search for improved energy-storage materials has revealed Li-and Na-rich intercalation compounds as promising high-capacity cathodes. They exhibit capacities in excess of what would be expected from alkali-ion removal/reinsertion and charge compensation by transition-metal (TM) ions. The additional capacity is provided through charge compensation by oxygen redox chemistry and some oxygen loss. It has been reported previously that oxygen redox occurs in O 2p orbitals that interact with alkali ions in the TM and alkali-ion layers (that is, oxygen redox occurs in compounds containing Li+-O(2p)-Li+ interactions). Na2/3[Mg0.28Mn0.72]O2 exhibits an excess capacity and here we show that this is caused by oxygen redox, even though Mg2+ resides in the TM layers rather than alkali-metal (AM) ions, which demonstrates that excess AM ions are not required to activate oxygen redox. We also show that, unlike the alkali-rich compounds, Na2/3[Mg0.28Mn0.72]O2 does not lose oxygen. The extraction of alkali ions from the alkali and TM layers in the alkalirich compounds results in severely underbonded oxygen, which promotes oxygen loss, whereas Mg2+ remains in Na2/3[Mg0.28Mn0.72]O2, which stabilizes oxygen.
- Published
- 2018
- Full Text
- View/download PDF
8. Bulk O2formation and Mg displacement explain O-redox in Na0.67Mn0.72Mg0.28O2
- Author
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Boivin, Edouard, House, Robert A., Pérez-Osorio, Miguel A., Marie, John-Joseph, Maitra, Urmimala, Rees, Gregory J., and Bruce, Peter G.
- Abstract
O-redox in compounds with Li on the transition-metal layers (TML) has recently been attributed to the formation of molecular O2on charge, trapped in the lattice. Here, we show that a similar process occurs for P2-Na0.67[Mn0.72Mg0.28]O2, which contains Mg2+on the TML. The molecular O2is identified by high-resolution RIXS and quantified by magnetometry, showing that it equates to the charge passed. This O2is trapped in voids that are formed by Mg2+out-of-plane displacement and Mn4+in-plane disordering and is then reduced on discharge associated with a large voltage hysteresis. In contrast to compounds containing Li+in the TML, in which the honeycomb ordering and the high-voltage plateau are irreversibly lost after the first cycle, in P2-Na0.67[Mn0.72Mg0.28]O2, the plateau reappears partially on the second charge due to the partial reversibility of Mn in-plane and Mg out-of-plane migration and the local reformation of the honeycomb ordering.
- Published
- 2021
- Full Text
- View/download PDF
9. Van der Waals Interactions and Anharmonicity in the Lattice Vibrations, Dielectric Constants, Effective Charges, and Infrared Spectra of the Organic−Inorganic Halide Perovskite CH3NH3PbI3
- Author
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UCL - SST/IMCN/NAPS - Nanoscopic Physics, A. Pérez-Osorio, Miguel, Champagne, Aurélie, Zacharias, Marios, Rignanese, Gian-Marco, Giustino, Feliciano, UCL - SST/IMCN/NAPS - Nanoscopic Physics, A. Pérez-Osorio, Miguel, Champagne, Aurélie, Zacharias, Marios, Rignanese, Gian-Marco, and Giustino, Feliciano
- Abstract
Using first-principles calculations, we perform a comprehensive and systematic analysis to establish the role of van der Waals (vdW) interactions and anharmonicity in the vibrational properties of the low-temperature orthorhombic phase of the hybrid perovskite CH3NH3PbI3. To this end, we consider the most common approaches for including vdW effects in our phonon calculations: the semiempirical Grimme approximations, the Tkatchenko-Scheffler dispersion corrections, and the vdW density-functional method. The vibrational normal modes are first calculated within the harmonic approximation. We consider the LDA and GGA approximations to the exchange-correlation functional and include spin−orbit coupling (SOC) effects. On top of the harmonic calculations, we also evaluate the anharmonicity of the normal modes and the phonon−phonon coupling by solving one-dimensional and two-dimensional nuclear Schrödinger equations, respectively, via the finite-displacement method. We observe that both the LDA and GGA approximations work remarkably well in describing the vibrational properties of CH3NH3PbI3. We find that vdW effects and relativistic effects do not have any significant impact on the vibrational properties of CH3NH3PbI3. Our study also reveals that the spinning modes of the organic CH3NH3+ cations carry considerable anharmonicity but that the anharmonic coupling between different modes is relatively small.
- Published
- 2017
10. Electron–phonon coupling in hybrid lead halide perovskites
- Author
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Wright, Adam D., Verdi, Carla, Milot, Rebecca L., Eperon, Giles E., Pérez-Osorio, Miguel A., Snaith, Henry J., Giustino, Feliciano, Johnston, Michael B., and Herz, Laura M.
- Subjects
Condensed Matter::Materials Science ,Condensed Matter::Superconductivity ,Science ,Condensed Matter::Strongly Correlated Electrons ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect - Abstract
Phonon scattering limits charge transport in perovskite solar cells, yet the interactions involved are still poorly understood. Here, Wright et al. show by photoluminescence measurements and first-principles calculations that longitudinal optical phonons dominate the electron-phonon coupling at room temperature.
- Published
- 2016
- Full Text
- View/download PDF
11. Development and application of ab initio methods for the study of electronic excitations in molecules and extended solids: GW approximation and constrained DFT
- Author
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Pérez Osorio, Miguel Angel, Alonso Pruneda, José Miguel, Ordejón Rontomé, Pablo, and Universitat Autònoma de Barcelona. Departament de Química
- Subjects
Ciències Experimentals - Abstract
El objetivo principal de esta tesis fue la implementación dentro del código SIESTA de dos métodos de primeros principios para el estudio de excitaciones electrónicas en moléculas y sólidos extendidos. Los métodos son la aproximación GW y el ’constrained’ DFT. Los métodos fueron implementados usando bases de orbitales extrictamente localizados generadas por SIESTA. El uso de este tipo de orbitales abre la posibilidad de estudiar sistemas que contienen miles de átomos. La aproximación GW es un método derivado de la teoría de perturbaciones de muchos cuerpos para la funcin de Green de una partícula, que se usa para el cálculo de las energías de excitación de quasipart ículas. En este trabajo, se implementó el método propuesto por F. Giustino et al. [3], que solo requiere el uso de los estados electrónicos ocupados para calcular los ingredientes de esta aproximación: la función de Green y el potencial de Coulomb apantallado. En método de ’constrained’ DFT se impone una ligadura sobre la densidad electrnica del sistema a través de un potencial apropiado. En esta tesis se implementó una versión modificada de la aproximación propuesta por Q. Wu and T. Van Voorhis [4] para encontrar el potencial de ’constraining’ de manera eficiente. El método se extendió para el caso de sistemas periódicos. Como una aplicación del método, se estudiaron procesos de transferencia de carga en el conductor oránico TTF-TCNQ. Una aplicación interesante de los métodos implementados es el estudio de los procesos electrónicos que tienen lugar en las celdas solares y dispositivos fotovoltaicos. El material ms ampliamente usado en la fabriacin de estos dispositivos es el TiO2 en fase anatase dopada con impurezas de nitrógeno o sensibilizada con colorantes orgánicos. Como un paso previo al estudio de las excitaciones electrnicas de este material, se caracterizaron sus propiedades electrónicas, estructurales, t y vibracionales usando la teoría DFT. Además, se estudiaroon las energías ’binding’ de los niveles de core de las diferentes especies químicas., The main aim of this thesis is the implementation in the SIESTA code (a widely used academic computational program based on the density functional theory DFT for the simulation of materials) [1, 2] of two powerful methods for the study of electronic excitations in molecules and extended solids. The methods are the so-called constrained density functional theory (CDFT) and the GW approximation and they are implemented within the strictly localized orbital formalism as defined in SIESTA. The use of local bases opens the possibility of calculating electronic excitations in systems containing thousands of atoms. The GW approximation is a powerful method derived from manybody perturbation theory for the one-particle Green function to calculate quasiparticle excitation energies. We implement the approach proposed by F. Giustino et al. [3] that only requires the use of the occupied electronic states to compute the Green function and screened Coulomb interaction, and from which one constructs the self-energy operator, . In this approach, the Green function is approximated to that of a non-interacting electron system and calculated using a inhomogeneous linear system, while the dynamically screened potential is calculated through the self-consistent linear-response Sternheimer equation. Since the original equations were stated within the plane waves formalism, here we rewrite these equations for basis sets of strictly localized orbitals. As an application of our approach for the dynamically screened potential, we calculate the dielectric function of several insulating and semiconducting materials: LiCl, diamond, silicon and germanium, comparing our results with plane-waves calculations. In the constrained density functional theory, we impose a constraint upon the electronic density of a system through an appropriate potential (called constraining potential) to obtain a neutral excitation. We implement a modified version of the approach proposed by Q.Wu and T. Van Voorhis [4, 5, 6] to find the constraining potential efficiently. Moreover, we extend the method for the case of periodic solids. As an application of our CDFT method, we study the charge transfer between the TTF and TCNQ molecules in the TTF-TCNQ conducting organic salt, where it has been suggested from XPS experiments that the charge transfer process is dynamic, leading to the coexistence of TTF0-TCNQ0 and TTF1+-TCNQ1− charge states [7, 8]. An interesting potential application of our implemented methods is the study of electronic excitations in semiconductor-based solar cells and photovoltaic devices to the efficient design and fabrication of such devices [9, 10, 11]. One of the most extensively used materials for the fabrication of these devices is the anatase TiO2 whether doped with nitrogen impurities or sensitized with dye molecules. Using the DFT machinery we characterize this material as the first step before the calculation of their electronic excitations. We study native defects: oxygen vacancies and interstitial titanium, and nitrogen impurities at interstitial or substitutional position in the anatase matrix. The electronic, structural and thermodynamic properties of all these point defects with different charge states were calculated. Moreover, we study the lattice dynamic of defective anatase in order to determine how defects affect the vibrational modes of pristine anatase and what are the new features arising from defects. We calculate the binding energy shifts of the N 1s, O 1s and Ti 3p core levels to contribute to the full characterization of the defects. Our results of lattice dynamic and core level binding energy shifts are compared with experimental data from Raman and XPS spectroscopy, respectively.
- Published
- 2013
12. Development and application of ab initio methods for the study of electronic excitations in molecules and extended solids GW approximation and constrained DFT
- Author
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Pruneda, José Miguel Alonso, Ordejón Rontomé, Pablo, Pérez Osorio, Miguel Angel, Universitat Autònoma de Barcelona. Departament de Química, Pruneda, José Miguel Alonso, Ordejón Rontomé, Pablo, Pérez Osorio, Miguel Angel, and Universitat Autònoma de Barcelona. Departament de Química
- Abstract
El objetivo principal de esta tesis fue la implementación dentro del código SIESTA de dos métodos de primeros principios para el estudio de excitaciones electrónicas en moléculas y sólidos extendidos. Los métodos son la aproximación GW y el 'constrained' DFT. Los métodos fueron implementados usando bases de orbitales extrictamente localizados generadas por SIESTA. El uso de este tipo de orbitales abre la posibilidad de estudiar sistemas que contienen miles de átomos. La aproximación GW es un método derivado de la teoría de perturbaciones de muchos cuerpos para la funcin de Green de una partícula, que se usa para el cálculo de las energías de excitación de quasipart ículas. En este trabajo, se implementó el método propuesto por F. Giustino et al. [3], que solo requiere el uso de los estados electrónicos ocupados para calcular los ingredientes de esta aproximación: la función de Green y el potencial de Coulomb apantallado. En método de 'constrained' DFT se impone una ligadura sobre la densidad electrnica del sistema a través de un potencial apropiado. En esta tesis se implementó una versión modificada de la aproximación propuesta por Q. Wu and T. Van Voorhis [4] para encontrar el potencial de 'constraining' de manera eficiente. El método se extendió para el caso de sistemas periódicos. Como una aplicación del método, se estudiaron procesos de transferencia de carga en el conductor oránico TTF-TCNQ. Una aplicación interesante de los métodos implementados es el estudio de los procesos electrónicos que tienen lugar en las celdas solares y dispositivos fotovoltaicos. El material ms ampliamente usado en la fabriacin de estos dispositivos es el TiO2 en fase anatase dopada con impurezas de nitrógeno o sensibilizada con colorantes orgánicos. Como un paso previo al estudio de las excitaciones electrnicas de este material, se caracterizaron sus propiedades electrónicas, estructurales, t y vibracionales usando la teoría DFT. Además, se estudiaroon las energías 'binding' de los n, The main aim of this thesis is the implementation in the SIESTA code (a widely used academic computational program based on the density functional theory DFT for the simulation of materials) [1, 2] of two powerful methods for the study of electronic excitations in molecules and extended solids. The methods are the so-called constrained density functional theory (CDFT) and the GW approximation and they are implemented within the strictly localized orbital formalism as defined in SIESTA. The use of local bases opens the possibility of calculating electronic excitations in systems containing thousands of atoms. The GW approximation is a powerful method derived from manybody perturbation theory for the one-particle Green function to calculate quasiparticle excitation energies. We implement the approach proposed by F. Giustino et al. [3] that only requires the use of the occupied electronic states to compute the Green function and screened Coulomb interaction, and from which one constructs the self-energy operator, . In this approach, the Green function is approximated to that of a non-interacting electron system and calculated using a inhomogeneous linear system, while the dynamically screened potential is calculated through the self-consistent linear-response Sternheimer equation. Since the original equations were stated within the plane waves formalism, here we rewrite these equations for basis sets of strictly localized orbitals. As an application of our approach for the dynamically screened potential, we calculate the dielectric function of several insulating and semiconducting materials: LiCl, diamond, silicon and germanium, comparing our results with plane-waves calculations. In the constrained density functional theory, we impose a constraint upon the electronic density of a system through an appropriate potential (called constraining potential) to obtain a neutral excitation. We implement a modified version of the approach proposed by Q.Wu and T. Van Voorhis [4
- Published
- 2013
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