27 results on '"Diego Guedes-Sobrinho"'
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2. Investigating Molecular Adsorption on Graphene-Supported Platinum Subnanoclusters: Insights from DFT + D3 Calculations
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João Paulo Cerqueira Felix, Gabriel Reynald da Silva, Glaucio R. Nagurniak, Alexandre C Dias, Renato P Orenha, Celso R. C. Rêgo, Renato L. T. Parreira, Diego Guedes-Sobrinho, and Maurício J. Piotrowski
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Chemistry ,QD1-999 - Published
- 2024
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3. Automated workflow for analyzing thermodynamic stability in polymorphic perovskite alloys
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Luis Octavio de Araujo, Celso R. C. Rêgo, Wolfgang Wenzel, Maurício Jeomar Piotrowski, Alexandre Cavalheiro Dias, and Diego Guedes-Sobrinho
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Materials of engineering and construction. Mechanics of materials ,TA401-492 ,Computer software ,QA76.75-76.765 - Abstract
Abstract In this first-principles investigation, we explore the polymorphic features of pseudo-cubic alloys, focusing on the impact of mixing organic and inorganic cations on their structural and electronic properties, configurational disorder, and thermodynamic stability. Employing an automated cluster expansion within the generalized quasichemical approximation (GQCA), our results reveal how the effective radius of the organic cation (r MA = 2.15 Å, r FA = 2.53 Å) and its dipole moment (μ MA = 2.15 D, μ FA = 0.25 D), influences Glazer’s rotations in the A1−x Cs x PbI3 (A = MA, FA) sublattice, with MA-based alloy presenting a higher critical temperature (527 K) and being stable for x > 0.60 above 200 K, while its FA analog has a lower critical temperature (427.7 K) and is stable for x
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- 2024
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4. Unveiling excitons in two-dimensional $$\beta$$ β -pnictogens
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Marcos R. Guassi, Rafael Besse, Maurício J. Piotrowski, Celso R. C. Rêgo, Diego Guedes-Sobrinho, Andréia Luisa da Rosa, and Alexandre Cavalheiro Dias
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2D materials ,Pnictogens ,Excitons ,Density-functional theory ,Bethe–Salpeter equation ,Medicine ,Science - Abstract
Abstract In this paper, we investigate the optical, electronic, vibrational, and excitonic properties of four two-dimensional $$\beta$$ β -pnictogen materials—nitrogenene, phosphorene, arsenene, and antimonene—via density functional theory calculations and the Bethe–Salpeter equation. These materials possess indirect gaps with significant exciton binding energies, demonstrating isotropic behavior under circular light polarization and anisotropic behavior under linear polarization by absorbing light within the visible solar spectrum (except for nitrogenene). Furthermore, we observed that Raman frequencies red-shift in heavier pnictogen atoms aligning with experimental observations; simultaneously, quasi-particle effects notably influence the linear optical response intensively. These monolayers’ excitonic effects lead to optical band gaps optimized for solar energy harvesting, positioning them as promising candidates for advanced optoelectronic device applications.
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- 2024
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5. Unveiling oxygen vacancy impact on lizardite thermo and mechanical properties
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H. Pecinatto, Celso R. C. Rêgo, W. Wenzel, C. A. Frota, B. M. S. Perrone, Maurício J. Piotrowski, Diego Guedes-Sobrinho, Alexandre C. Dias, Cicero Mota, M. S. S. Gusmão, and H. O. Frota
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Medicine ,Science - Abstract
Abstract Here, we performed a systematic DFT study assisted by the workflow framework SimStack for the mechanical and thermodynamic properties of the clay mineral lizardite in pristine and six different types of O vacancies configurations. In most cases, the defect caused a structural phase transition in the lizardite from the trigonal (pristine) to the triclinic phase. The results show that oxygen vacancies in lizardite significantly reduce the lattice thermal conductivity, accompanied by an elastic moduli reduction and an anisotropy index increase. Through the P–V relation, an increase in compressibility was evidenced for vacancy configurations. Except for the vacancy with the same crystalline structure as pristine lizardite, the sound velocities of the other vacancy configurations produce a decrease in these velocities, and it is essential to highlight high values for the Grüneisen parameter. We emphasize the great relevance of the punctual-defects introduction, such as O vacancies, in lizardite, since this microstructural design is responsible for the decrease of the lattice thermal conductivity in comparison with the pristine system by decreasing the heat transfer ability, turning lizardite into a promising candidate for thermoelectric materials
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- 2023
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6. Revealing the impact of organic spacers and cavity cations on quasi-2D perovskites via computational simulations
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Diego Guedes-Sobrinho, Danilo Neves Silveira, Luis O. de Araujo, Jônatas Favotto Dalmedico, W. Wenzel, Y. Pramudya, Maurício J. Piotrowski, and Celso R. C. Rêgo
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Medicine ,Science - Abstract
Abstract Two-dimensional hybrid lead iodide perovskites based on methylammonium (MA) cation and butylammonium (BA) organic spacer—such as $${\hbox {BA}_{2}\hbox {MA}_{n-1}\hbox {Pb}_{n}\hbox {I}_{3n+1}}$$ BA 2 MA n - 1 Pb n I 3 n + 1 —are one of the most explored 2D hybrid perovskites in recent years. Correlating the atomistic profile of these systems with their optoelectronic properties is a challenge for theoretical approaches. Here, we employed first-principles calculations via density functional theory to show how the cation partially canceled dipole moments through the $${{\hbox {NH}_{3}}^{+}}$$ NH 3 + terminal impact the structural/electronic properties of the $${\hbox {Pb}_{n}\hbox {I}_{3n+1}}$$ Pb n I 3 n + 1 sublattices. Even though it is known that at high temperatures, the organic cation assumes a spherical-like configuration due to the rotation of the cations inside the cage, our results discuss the correct relative orientation according to the dipole moments for ab initio simulations at 0 K, correlating well structural and electronic properties with experiments. Based on the combination of relativistic quasiparticle correction and spin-orbit coupling, we found that the MA horizontal-like configuration concerning the inorganic sublattice surface leads to the best relationship between calculated and experimental gap energy throughout n = 1, 2, 3, 4, and 5 number of layers. Conversely, the dipole moments cancellation (as in BA-MA aligned-like configuration) promotes the closing of the gap energies through an electron depletion mechanism. We found that the anisotropy $$\rightarrow$$ → isotropy optical absorption conversion (as a bulk convergence) is achieved only for the MA horizontal-like configuration, which suggests that this configuration contribution is the majority in a scenario under temperature effects.
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- 2023
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7. How cation nature controls the bandgap and bulk Rashba splitting of halide perovskites
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Luis Octavio de Araujo, Celso R. C. Rêgo, W. Wenzel, Danilo N. Silveira, Maurício J. Piotrowski, Fernando P. Sabino, Yohanes Pramudya, and Diego Guedes‐Sobrinho
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Computational Mathematics ,General Chemistry - Published
- 2023
8. Molecular adsorption on coinage metal subnanoclusters: A DFT+D3 investigation
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João P. C. S. Felix, Krys E. A. Batista, Wesley O. Morais, Glaucio R. Nagurniak, Renato P. Orenha, Celso R. C. Rêgo, Diego Guedes‐Sobrinho, Renato L. T. Parreira, Mateus M. Ferrer, and Maurício J. Piotrowski
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Computational Mathematics ,General Chemistry - Abstract
Gold and silver subnanoclusters with few atoms are prominent candidates for catalysis-related applications, primarily because of the large fraction of lower-coordinated atoms exposed and ready to interact with external chemical species. However, an in-depth energetic analysis is necessary to characterize the relevant terms within the molecular adsorption process that can frame the interactions within the Sabatier principle. Herein, we investigate the interaction between Ag
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- 2022
9. Bulk Rashba Effect Splitting and Suppression in Polymorphs of Metal Iodine Perovskites
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Fernando P. Sabino, Celso R. C. Rêgo, Luis Octavio de Araujo, and Diego Guedes-Sobrinho
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Materials science ,Condensed matter physics ,Metal ,Condensed Matter::Materials Science ,Tetragonal crystal system ,Octahedron ,visual_art ,visual_art.visual_art_medium ,Quasiparticle ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Orthorhombic crystal system ,Symmetry breaking ,Physical and Theoretical Chemistry ,Polarization (electrochemistry) ,Rashba effect - Abstract
We quantified the bulk Rashba splitting and suppression in polymorphs of MA(Pb, Sn, Ge, or Si)I3 perovskites. The low-computational-cost DFT-1/2 quasiparticle correction was performed for all structures, combined with the inclusion of spin-orbit coupling (SOC) effects. The presence of SOC and symmetry breaking from the metal off-centering octahedral distortion are indispensable and essential conditions for Rashba splitting, whose magnitude emerges from the Pb → Si sequence. Additionally, the quasiparticle correction provides energy bandgaps for MAPbI3 (cubic, tetragonal, and orthorhombic), MASnI3 (cubic and tetragonal), and MAGeI3 (cubic) that are in outstanding agreement with experimental results. However, while gap energies are yielded collaboratively from the metal off-centering and relative octahedral tiltings, the bulk Rashba suppression is reached for metal on-centering (octahedral platonic-like) configurations that are thermodynamically stable even when the charge polarization is kept invariant among metal-I bonds in the polymorphs.
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- 2021
10. The effect of different energy portions on the 2D/ 3D stability swapping for 13-atom metal clusters†
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Diego Guedes-Sobrinho, Renato P. Orenha, Renato L. T. Parreira, Glaucio R. Nagurniak, Gabriel Reynald Da Silva, and Maurício J. Piotrowski
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Ag13 ,metal clusters ,2D/3D stability ,CIENCIAS EXATAS E DA TERRA::QUIMICA [CNPQ] ,General Physics and Astronomy ,Physical and Theoretical Chemistry ,Au13 ,Cu13 - Abstract
The complexity of Cu13, Ag13, and Au13 coinage-metal clusters was investigated through their energy contributions via a density functional theory study, considering improvements in the PBE functional, such as van der Waals (vdW) corrections, spin–orbit coupling (SOC), Hubbard term (+U), and their combinations. Investigating two-dimensional (planar 2D) and three-dimensional (distorted 3D, CUB – cuboctahedral, and ICO – icosahedral) configurations, we found that vdW corrections are dominant in modulating the stability swapping between 2D and ICO (3D) for Ag13 (Au13), whereas for Cu13 its role is increasing the relative stability between 2D (least stable) and 3D (most stable), setting ICO as the reference. Among the energy portions that constitute the relative total energy, the dimensionality difference correlates with the magnitude of the relative dispersion energy (large for 2D/ICO and small for 3D/ICO) as the causal factor responsible for an eventual stability swapping. For instance, empirical vdW corrections may favor Ag13 as ICO, while semi empirical ones tend to swap the stability by favoring 2D. The same tendency is observed for Au13, except when SOC is included, which enlarges the stability of 3D over 2D. Energy decomposition analysis combined with the natural orbitals for the chemical valence approach confirmed the correlations between the dimensionality difference and the magnitude of the relative dispersion energies. Our structural analysis protocol was able to capture the local distortion effects (or even their absence) through the quantification of the Hausdorff chirality measure. Here, ICO, CUB, and 2D are achiral configurations for all coinage-metal clusters, whereas Cu13 as 3D presents a slight chirality when vdW correction based on many body dispersion is used, at the same time Ag13 as 3D turned out to be chiral for all calculation protocols as evidence of the role of the chemical composition. Palavras-chave: metal clusters, Au13, Ag13, Cu13, 2D/3D stability
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- 2022
11. Impact of the Polymorphism and Relativistic Effects on the Electronic Properties of Inorganic Metal Halide Perovskites
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Luis Octavio de Araujo, Celso R. C. Rêgo, W. Wenzel, Fernando P. Sabino, and Diego Guedes-Sobrinho
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Technology ,General Energy ,Physical and Theoretical Chemistry ,ddc:600 ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Published
- 2022
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12. Assessment of the van der Waals, Hubbard U parameter and spin-orbit coupling corrections on the 2D/3D structures from metal gold congeners clusters
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Maurício J, Piotrowski, Renato P, Orenha, Renato L T, Parreira, and Diego, Guedes-Sobrinho
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The coinage-metal clusters possess a natural complexity in their theoretical treatment that may be accompanied by inherent shortcomings in the methodological approach. Herein, we performed a scalar-relativistic density functional theory study, considering Perdew, Burke, and Ernzerhof (PBE) with (empirical and semi empirical) van der Waals (vdW), spin-orbit coupling (SOC), +U (Hubbard term), and their combinations, to treat the
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- 2021
13. (Meta-)stability and Core–Shell Dynamics of Gold Nanoclusters at Finite Temperature
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Luca M. Ghiringhelli, Diego Guedes-Sobrinho, Weiqi Wang, Ian P. Hamilton, and Juarez L. F. Da Silva
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Range (particle radiation) ,Letter ,Materials science ,Shell (structure) ,02 engineering and technology ,Atmospheric temperature range ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Stability (probability) ,0104 chemical sciences ,Nanoclusters ,Amorphous solid ,Planar ,Chemical physics ,Substructure ,General Materials Science ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
Gold nanoclusters have been the focus of numerous computational studies, but an atomistic understanding of their structural and dynamical properties at finite temperature is far from satisfactory. To address this deficiency, we investigate gold nanoclusters via ab initio molecular dynamics, in a range of sizes where a core-shell morphology is observed. We analyze their structure and dynamics using state-of-the-art techniques, including unsupervised machine-learning nonlinear dimensionality reduction (sketch-map) for describing the similarities and differences among the range of sampled configurations. In the examined temperature range between 300 and 600 K, we find that whereas the gold nanoclusters exhibit continuous structural rearrangement, they are not amorphous. Instead, they clearly show persistent motifs: a cationic core of 1-5 atoms is loosely bound to a shell which typically displays a substructure resulting from the competition between locally spherical versus planar fragments. Besides illuminating the properties of core-shell gold nanoclusters, the present study proposes a set of useful tools for understanding their nature in operando.
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- 2019
14. Physical and Chemical Properties of Unsupported (MO2)n Clusters for M = Ti, Zr, or Ce and n = 1–15: A Density Functional Theory Study Combined with the Tree-Growth Scheme and Euclidean Similarity Distance Algorithm
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Yohanna Seminovski, Diego Guedes-Sobrinho, Israel Rosalino, Juarez L. F. Da Silva, and Larissa Zibordi-Besse
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Physics ,Work (thermodynamics) ,Ab initio ,02 engineering and technology ,Function (mathematics) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Similarity distance ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Tree (descriptive set theory) ,General Energy ,Scheme (mathematics) ,Euclidean geometry ,Density functional theory ,Physical and Theoretical Chemistry ,0210 nano-technology ,Algorithm - Abstract
Metal-oxide clusters, (MO2)n, have been widely studied along the years by experimental and theoretical techniques, however, our atomistic knowledge is still far from satisfactory for systems such as ZrO2 and CeO2, which play a crucial role in nanocatalysis. Thus, with the aim to improve our atomistic understanding of the physical and chemical properties of the metal-oxide clusters as a function of size, n, we performed a systematic ab initio density functional theory study of the (MO2)n clusters, where M = Ti, Zr, or Ce and n = 1–15. In this work, the trial atomic configurations were obtained by a tree-growth (TG) scheme combined with the Euclidean similarity distance (ESD) algorithm. Using the (TiO2)n clusters, we validated the TG-ESD algorithm, which found the same putative global minimum configurations (pGMCs) reported in the literature for most of the (TiO2)n systems, and in a few cases, there are lower energy configurations than previous data. From our analyses, the structural parameters of the (MO2)...
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- 2018
15. Ab Initio Investigation of Atomistic Insights into the Nanoflake Formation of Transition-Metal Dichalcogenides: The Examples of MoS2, MoSe2, and MoTe2
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Augusto C. H. Da Silva, Naidel A. M. S. Caturello, Rafael Besse, Matheus P. Lima, Diego Guedes-Sobrinho, and Juarez L. F. Da Silva
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Materials science ,Ab initio ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Similarity distance ,01 natural sciences ,Square pyramidal molecular geometry ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,General Energy ,Transition metal ,Octahedron ,Chemical physics ,Tetrahedron ,Density functional theory ,Physical and Theoretical Chemistry ,0210 nano-technology ,Electronic properties - Abstract
An atom-level understanding of the evolution of the physical and chemical properties of transition-metal dichalcogenide (TMD) nanoflakes is a key step to improve our knowledge of two-dimensional (2D) TMD materials, which can help in the designing of new 2D materials. Here, we report a density functional theory (DFT) study of the evolution of the structural, energetic, and electronic properties of (MoQ2)n nanoflakes, where Q = S, Se, and Te and n = 1–16. All optimized DFT configurations for each system (10n) were generated by an in-house implementation of the tree-growth scheme combined with the modified Euclidean similarity distance algorithm, which reduces a large set configurations (10n million) to 10n trial structures. We found that the energetic favored configurations change between two sorts of clusters: frameworks elongated in one dimension with tetrahedral and square pyramidal coordination of Mo atoms, which is followed by 2D nanoflakes with tetrahedral, square pyramidal, and distorted octahedral c...
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- 2018
16. Size-Induced Phase Evolution of MoSe2 Nanoflakes Revealed by Density Functional Theory
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Rafael Besse, Diego Guedes-Sobrinho, Juarez L. F. Da Silva, Naidel A. M. S. Caturello, Carlos M. O. Bastos, Matheus P. Lima, and Guilherme Matos Sipahi
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Materials science ,Peierls transition ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Trigonal prismatic molecular geometry ,01 natural sciences ,Phase evolution ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Crystallography ,General Energy ,Octahedron ,Phase (matter) ,Density functional theory ,Physical and Theoretical Chemistry ,0210 nano-technology ,Parallelogram ,Stoichiometry - Abstract
The control of the relative stability between trigonal prismatic and octahedral structures in transition-metal dichalcogenides (TMDs) is an important step toward technological applications of 2D TMDs materials, where the electronic properties have a strong dependence on the structural phase and size effects. We report a density functional theory investigation of the size effect on the relative phase stability of stoichiometric (MoSe2)n nanoflakes with parallelogram shape for n = 15, 63, 108, 130, 154, 192. We found that the octahedral phase adopts a distorted configuration, which is driven by the Peierls transition mechanism, and, as expected, the Mo-terminated edges of the trigonal prismatic nanoflakes exhibit a strong reconstruction. Furthermore, for the smallest nanoflakes, the octahedral phase has the lowest energy, but with increasing the nanoflake size, the trigonal prismatic phase becomes the most stable. From our results and analyses, this transition is shown to be mainly caused by a difference in...
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- 2018
17. Ab Initio Investigation of the Role of CO Adsorption on the Physical Properties of 55-Atom PtCo Nanoalloys
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Diego Guedes-Sobrinho, Rafael L. H. Freire, Anderson S. Chaves, and Juarez L. F. Da Silva
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Work (thermodynamics) ,Chemistry ,Ab initio ,Nanoparticle ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,General Energy ,Adsorption ,Chemical physics ,Computational chemistry ,Atom ,Molecule ,Density functional theory ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
The knowledge of the physical and chemical properties of PtCo nanoparticles as a function of the Pt/Co composition and atomic distribution is crucial for several potential applications, which includes catalysis, anticorrosion, data storage, etc. However, our current atom-level understanding is far from satisfactory, in particular due to the challenges to take into account chemical environment effects. In this work, we report a density functional theory investigation of the structural, energetic, and electronic properties of binary 55-atom PtCo particles at a saturated CO atmosphere (31 molecules), i.e., (CO)31/PtnCo55–n. For PtCo in the gas phase, which adopts an icosahedron-like (ICO-like) structure in the lowest-energy configurations for all studied compositions, we found a rough correlation between stability and the number of bonds among the Pt and Co species; i.e., the stability (excess energy) increases (decreases) by increasing the number of Pt and Co bonds and with a minimum at about n = 28–42 (Pt-...
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- 2017
18. Theoretical Study of the Structural, Energetic, and Electronic Properties of 55-Atom Metal Nanoclusters: A DFT Investigation within van der Waals Corrections, Spin–Orbit Coupling, and PBE+U of 42 Metal Systems
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Diego Guedes-Sobrinho, Maurício J. Piotrowski, Krys E. A. Batista, Juarez L. F. Da Silva, Crina Georgeta Ungureanu, Anderson S. Chaves, and Polina Tereshchuk
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Valence (chemistry) ,Chemistry ,Ab initio ,02 engineering and technology ,Spin–orbit interaction ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Nanoclusters ,Metal ,symbols.namesake ,General Energy ,Computational chemistry ,Chemical physics ,visual_art ,visual_art.visual_art_medium ,symbols ,Density functional theory ,Physical and Theoretical Chemistry ,van der Waals force ,0210 nano-technology ,Electronic properties - Abstract
An atom-level ab initio understanding of the structural, energetic, and electronic properties of nanoclusters with diameter size from 1 to 2 nm figures as a prerequisite to foster their potential technological applications. However, because of several challenges such as the identification of ground-state structures by experimental and theoretical techniques, our understanding is still far from satisfactory, and further studies are required. We report a systematic ab initio investigation of the 55-atom metal nanoclusters, (M55), including alkaline, transitional, and post-transitional metals, that is, a total of 42 systems. Our calculations are based on all-electron density functional theory within the Perdew–Burke–Ernzerhof (PBE) functional combined with van der Waals (vdW) correction, spin–orbit coupling (SOC) for the valence states. Furthermore, we also investigated the role of the localization of the d states by using the PBE+U functional. We found a strong preference for the putative PBE global-minimum...
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- 2016
19. Thermodynamic Stability and Structural Insights for CH3NH3Pb1−xSixI3, CH3NH3Pb1−xGexI3, and CH3NH3Pb1−xSnxI3 Hybrid Perovskite Alloys: A Statistical Approach from First Principles Calculations
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Ivan Guilhon, Lara K. Teles, Diego Guedes-Sobrinho, and Marcelo Marques
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0301 basic medicine ,Materials science ,Alloy ,Iodide ,lcsh:Medicine ,engineering.material ,Miscibility ,Article ,Metal ,03 medical and health sciences ,0302 clinical medicine ,lcsh:Science ,Perovskite (structure) ,chemistry.chemical_classification ,Multidisciplinary ,Structural properties ,lcsh:R ,030104 developmental biology ,Sustainability ,chemistry ,visual_art ,Excited state ,engineering ,visual_art.visual_art_medium ,Thermodynamics ,Physical chemistry ,lcsh:Q ,Chemical stability ,Density functional theory ,030217 neurology & neurosurgery - Abstract
The recent reaching of 20% of conversion efficiency by solar cells based on metal hybrid perovskites (MHP), e.g., the methylammonium (MA) lead iodide, CH3NH3PbI3 (MAPbI3), has excited the scientific community devoted to the photovoltaic materials. However, the toxicity of Pb is a hindrance for large scale commercial of MHP and motivates the search of another congener eco-friendly metal. Here, we employed first-principles calculations via density functional theory combined with the generalized quasichemical approximation to investigate the structural, thermodynamic, and ordering properties of MAPb1−xSixI3, MAPb1−xGexI3, and MAPb1−xSnxI3 alloys as pseudo-cubic structures. The inclusion of a smaller second metal, as Si and Ge, strongly affects the structural properties, reducing the cavity volume occupied by the organic cation and limitating the free orientation under high temperature effects. Unstable and metaestable phases are observed at room temperature for MAPb1−xSixI3, whereas MAPb1−xGexI3 is energetically favored for Pb-rich in ordered phases even at very low temperatures. Conversely, the high miscibility of Pb and Sn into MAPb1−xSnxI3 yields an alloy energetically favored as a pseudo-cubic random alloy with tunable properties at room temperature.
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- 2019
20. Relativistic DFT-1/2 Calculations Combined with a Statistical Approach for Electronic and Optical Properties of Mixed Metal Hybrid Perovskites
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Lara K. Teles, Diego Guedes-Sobrinho, Marcelo Marques, and Ivan Guilhon
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010302 applied physics ,Coupling ,Physics ,Mixed metal ,Condensed matter physics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter::Superconductivity ,0103 physical sciences ,Quasiparticle ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,DISPOSITIVOS ELETRÔNICOS ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
We overcome the great theoretical computational challenge of mixed perovskites, providing a rigorous and efficient model by including quasiparticle, spin-orbit coupling, and disorder effects. As a benchmark, we consider the mixed MAPb
- Published
- 2019
21. Influence of electrosynthesis methods in the electrocatalytical and morphological properties of cobalt and nickel hexacyanoferrate films
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Thais Schroeder Rossi, Diego Guedes-Sobrinho, Herbert Winnischofer, Luciane Novaes Tenório, and Marcio Vidotti
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Prussian blue ,Materials science ,General Chemical Engineering ,chemistry.chemical_element ,Nanoparticle ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrosynthesis ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,Nickel ,chemistry ,Chemical engineering ,Surface modification ,Thin film ,0210 nano-technology ,Cobalt - Abstract
Prussian Blue analogues (PBA) based on Cobalt and Nickel thin films were assembled by two distinct methodologies using direct electroprecipitation on the substrate and metallic nanoparticle surface modification. The modified electrodes were characterized by several techniques such as Infrared Reflection-Absorption and Electrochemical Impedance Spectroscopies, Scanning Electron and Atomic Force Microscopies, and Electrochemical methods. The electrocatalytical properties of the films were also evaluated and the rate constants for thiosulfate oxidation were obtained and discussed. The results pointed out that the metallic nanoparticle approach has presented higher electrocatalytic effect, suggesting this methodology towards the construction of high performance electrochemical based devices such as sensors, biosensors, fuel cells and others.
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- 2020
22. Estudo ab initio dos efeitos de ligantes e temperatura na estabilidade e meta-estabilidade de nanoclusters metálicos
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Diego Guedes Sobrinho
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- 2018
23. Ab initio Study of the Ligands and Temperature Effects on the Stability and Meta-stability of Metallic Nanoclusters
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Diego Guedes Sobrinho, Juarez Lopes Ferreira da Silva, Eudes Eterno Fileti, Ricardo Paupitz Barbosa dos Santos, Albérico Borges Ferreira da Silva, and Lara Kuhl Teles
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Nanoclusters de metais de transição (TM) com dimensões de ~1,0 nm têm atraído grande interesse em diversas aplicações tecnológicas, como microeletrônica, óptica, dispositivos magnéticos e principalmente como nanocatalisadores. Nesse contexto, a morfologia desses sistemas é um fator fundamental para otimzação de performace nessas aplicações, tendo em vista a relação direta entre as propriedades físico-químicas e a estrutura atômica do nanocluster determinada pelas condições do ambiente (temperatura e moléculas adsorvidas). No entanto, diante das limitações relativas à precisão das técnicas de caracterização experimental disponíveis atualmente, sobretudo em dimensões nanométricas, o uso de cálculos computacionais através de métodos de primeiros princípios (ab initio) e baseados na teoria do funcional da densidade se torna indispensável. Neste trabalho, foram investigados os efeitos de ligantes e temperaturas nas propriedades estruturais, eletrônicas, estabilidade e meta-estabilidade de nanoclusters de TM. (i) Os efeitos de ligantes de (PH3)n e (SH2)n (saturação gradativa em n = 1, 6, 12 e 18) adsorvidos em nanoclusters unários de Pt55 e Au55 com estruturas icosaédricas (ICO), cuboctaédricas (CUB) e desordenadas de core reduzido (DRC) foram estudados a 0K. Em fase gasosa, as estruturas DRC com 7 e 9 átomos na região do core são 5,34 eV (Pt55) e 2,20 eV (Au55) mais estáveis que modelo ICO com simetria Ih com 13 átomos no core. Os resultados mostraram que existe uma forte compressão do core catiônico pela superfície aniônica induzida por interações de Coulomb (core+-superfície-), levando ao colapso e redução de estresse das estruturas simétricas a partir da redução do número de átomos na região do core. No entanto, a estabilidade da estrutura ICO aumenta com o aumento do número de moléculas adsorvidas, de modo que DRC e ICO se tornam energeticamente degeneradas em < 0,5 eV. Além disso, a adição de ligantes na superfície aniônica reduz a transferência de cargas entre as regiões de core+-superfície-, contribuindo para a redução das interações de Coulomb e, consequentemente, aliviando o estresse interno da estrutura ICO. Resultados similares foram obtidos utilizando ligantes de trifenilfosfina (PPh3), nos quais as longas cadeias carbônicas adicionam interações laterais entre os ligantes. (ii) Nanoclusters de binários de PtnCo(55 - n) a 0K mostraram alta estabilidade em todo intervalo de composições, indicando uma correlação direta entre estabilidade e distribuição homogênea de átomos de Pt e Co formando a nanoliga com estrutura ICO. No entanto, sob uma atmosfera saturada de ligantes de CO adsorvidos, a estabilidade da nanoliga diminui (aumenta) para composições com grandes quantidades de Pt (Co). As análises mostraram que sob os efeitos da adsorção as composições permanecem com configuração ICO, exceto para Pt42Co13 (estrutura core@shell do tipo Co@Pt em fase gasosa), onde as moléculas de CO deslocam os átomos de Co para a superfície, e, então, induzindo um processo de amorfização na formação de uma estrutura formada com átomos de Pt ocupando o core. Para investigar os efeitos de temperatura na estabilidade e meta-estabilidade de nanoclusters e clusters de Au utilizando dinâmica molecular de Born-Oppenheimer, foram utilizados nanoclusters de tamanho médio de Au25, Au38 e Au40 em fase gasosa e clusters de Au13 sob diferentes atmosferas saturadas de CO. (iii) Observou-se que em temperaturas de 300, 400, 500 e 600 K os nanoclusters exibem estruturas dinâmicas para as regiões de core-superfície, com core tetraédrico (4 átomos) ou T-bipiramidal (5 átomos) catiônicos fracamente ligados à superfície aniônica flexível. Uma abordagem estatística através de um algoritmo de redução de dimensionalidades para representação no espaço euclideano bidimensional, chamado de sketch-map, foi proposta como uma nova linguagem para analisar a superfície de energia livre (FES) dos sistemas calculada na aproximação de multistate Bennet acceptance-ratio. A FES foi utilizada como uma análise qualitativa das configurações estáveis e meta-estáveis sob os efeitos de temperaturas, indicando as regiões preferenciais do espaço configuracional de cada nanocluster investigado. (iv) Incluindo os efeitos de ligantes e temperaturas em clusters de Au13, foi observado que em altas temperaturas os clusters de Au13 em fase gasosa tendem a configurações mais abertas com menor comprimento de ligação com relação às estruturas tridimensionais. Por outro lado, a saturação do ambiente com ligantes de CO restringem a mobilidade dos átomos nos clusters de Au13, favorecendo a amostragem de estruturas tridimensionais mesmo em temperaturas relativamente altas. A análise de população de cargas mostrou uma alta concentração de elétrons nos átomos de O, de modo que o forte catiônico dos clusters de Au13 leva ao aumento da coordenação atômica, contribuindo para a estabilização das estruturas mais tridimensionais. Transition metal nanoclusters (TM) with dimensions of ~1,0 nm have attracted great interest in various technological applications such as microelectronics, optics, magnetic devices and mainly as nanocatalysts. In this way, the morphology of these systems is a fundamental factor for optimization of performance in these applications, considering the direct relationship between the physicochemical properties and the atomic structure of the nanocluster determined by the ambient conditions (temperature and adsorbed molecules). In this sense, in view of the limitations on the precision of the experimental characterization techniques currently available, especially in nanometric dimensions, the use of computational calculations using first principles methods (ab initio) and based on the density functional theory is indispensable. Thus, in this work, the effects of binders and temperatures on the structural, electronic properties, stability and metastability of TM nanoclusters were investigated. (i) In this way, the (PH3)n and (SH2)n ligands effects with gradual saturation at n = 1, 6, 12 and 18 adsorbed onto nanoclusters Pt55 and Au55 with icosahedral (ICO), cuboctahedron (CUB), and distorted reduced core (DRC) structures were studied at 0K. In the gas phase, the DRC structures with 7 and 9 atoms in the core region are 5,34 eV (Pt55) and 2,20 eV (Au55) more stable than ICO model with symmetry Ih with 13 atoms in core. The results showed that there is a strong compression of the cationic core by the anionic surface induced by interactions of Coulomb (core+-surface-), leading to collapse and stress reduction of the symmetrical structures from the reduction of the number of atoms in the core region. However, the stability of the ICO structure increases with increasing Number of molecules adsorbed, so that DRC and ICO become approximately degenerated in energy in < 0,5 eV. In addition, ligands on the anionic surface reduces the transfer of charges between core+- surface-, contributing to the reduction of interactions of Coulomb and, consequently, alleviating the internal stress of the ICO. Similar result were obtained using triphenylphosphine (PPh3) as large ligands, in which the long carbon chains add side interactions between the ligands. (ii) PtnCo(55 - n) binares nanoclusters at 0K showed a high stability across the range of compositions, indicating a direct correlation between stability and homogeneous distribution of Pt and Co atoms forming the nanoalloys with ICO structure. However, under a saturated atmosphere of adsorbed CO ligands, the stability of the nanoaaloys decreases (increases) to compositions with large amounts of Pt (Co). Analyzes have shown that under the effects of adsorption the compositions remain with ICO configuration, except for Pt42Co13 (Co@Pt as core@shell in gas-phase), where Co molecules displace the Co atoms to the surface, and then inducing an amorphization process for a structure formed with Pt atoms occupying the core. To investigate the temperature effects on the stability and metastability of Au nanoclusters and clusters by using Born-Oppenheimer molecular dynamics, medium size nanoclusters of Au25, Au38, and Au40 were used in gas-phase and clusters of Au13 under different saturated atmospheres of CO. (iii) It has been observed that at temperatures of 300, 400, 500, and 600 K, the nanoclusters exhibit dynamic structures for the core-surface regions with cationic tetrahedral (4 atoms) or T-bipyramidal (5 atoms) cores weakly bound to the flexible anionic surface. A statistical approach using a dimensionality reduction algorithm for two-dimensional Euclidean space representation, called sketch-map, was proposed as a new language to analyze the free energy surface (FES) of the systems calculated on the approximation of multistate Bennet acceptance-ratio. The FES was used as a qualitative analysis of the stable and metastable configurations under the effect of temperature, indicating the preferred regions of the configurational space of each nanocluster investigated. (iv) By including the effects of ligands and temperatures on Au13 clusters, it was observed that at high temperatures the Au13 clusters in gas-phase tend to have more open configurations with less bond length relative to three-dimensional structures. On the other hand, the saturation of the environment with CO ligands restricts the mobility of the atoms in Au13 clusters, favoring the sampling of three-dimensional structures even at temperatures relatively high. The charge population analysis showed a high concentration of electrons in the O atoms, so that the strong cationic character of the Au13 clusters leads to increased atomic coordination, contributing to the stabilization of the more three-dimensional.
- Published
- 2017
24. Density functional investigation of the adsorption effects of PH
- Author
-
Diego, Guedes-Sobrinho, Anderson S, Chaves, Maurício J, Piotrowski, and Juarez L F, Da Silva
- Abstract
Although several studies have been reported for Pt
- Published
- 2017
25. Correction: Nanocrystals self-assembled in superlattices directed by the solvent–organic capping interaction
- Author
-
Edson R. Leite, Antonio N. Pinheiro, Cleocir José Dalmaschio, André Farias de Moura, Diego Guedes Sobrinho, and Edney Geraldo da Silveira Firmiano
- Subjects
Solvent ,Materials science ,Nanocrystal ,Superlattice ,General Materials Science ,Nanotechnology ,Nanoscopic scale ,Self assembled - Abstract
Correction for ‘Nanocrystals self-assembled in superlattices directed by the solvent–organic capping interaction’ by Cleocir José Dalmaschio et al., Nanoscale, 2013, 5, 5602–5610.
- Published
- 2018
26. Theoretical investigation of the adsorption properties of CO, NO, and OH on monometallic and bimetallic 13-atom clusters: the example of Cu13, Pt7Cu6, and Pt13
- Author
-
Juarez L. F. Da Silva, Diego Guedes-Sobrinho, Maurício J. Piotrowski, and Anderson S. Chaves
- Subjects
Adsorption ,Chemistry ,Atom ,Inorganic chemistry ,Cationic polymerization ,Cluster (physics) ,Physical chemistry ,QUÍMICA QUÂNTICA ,Density functional theory ,Physical and Theoretical Chemistry ,Bimetallic strip ,Adsorption energy - Abstract
We report a density functional theory investigation of the adsorption properties of CO, NO, and OH on the Cu13, Pt7Cu6, and Pt13 clusters in the cationic, neutral, and anionic states with the aim to improve our atomistic understanding of the adsorption properties on bimetallic clusters compared with monometallic clusters. The adsorption energy of CO and NO are substantially stronger on Pt13 than on Cu13, and hence, CO and NO bind preferentially on Pt sites on Pt7Cu6. Thus, it can contribute to drive the migration of the Pt atoms from the core to the surface region in large PtCu nanoalloys. The CO and NO adsorption energies on the bimetallic cluster are enhanced by a few percent compared with the energies of the monometallic clusters, which shows that the Pt-Cu interaction can contribute to an increase in the adsorption energy. In contrast with CO and NO trends, the OH adsorption energies on Cu13, Pt7Cu6, and Pt13 deviates only up to 0.31 eV, and hence, there is no clear preference for Cu or Pt sites on Pt7Cu6 or an enhancement of the adsorption energy on the bimetallic systems. We found a reduction of the CO and NO vibrational frequencies upon adsorption, which indicates a weakening of the CO and NO binding energies, and it is supported by a slight increase in the bond lengths. However, the OH vibrational frequency increases upon adsorption, which indicates an enhancement of the OH binding energy, which is supported by a slight decrease in the bond length by about 0.01 Å. It can be explained by the large charge transfer from the clusters to the O atom, which enhances the electrostatic interaction in the O-H bonding.
- Published
- 2015
27. Nanocrystals self-assembled in superlattices directed by the solvent-organic capping interaction
- Author
-
Edney Geraldo da Silveira Firmiano, Antonio N. Pinheiro, Edson R. Leite, Diego Guedes Sobrinho, André Farias de Moura, and Cleocir José Dalmaschio
- Subjects
Solvent ,chemistry.chemical_compound ,Colloid ,chemistry ,Chemical engineering ,Benzyl alcohol ,Nanoparticle ,General Materials Science ,Nanotechnology ,Solubility ,Thin film ,Dip-coating ,Layer (electronics) - Abstract
Close-packed arrays of ZrO2 nanocrystals (NCs) have been self-assembled from a colloidal solution in a withdrawal dip coating process. A benzyl alcohol route was used to obtain NCs of narrowly controlled size, and then the capping layer was replaced by oleate using solvothermal treatment. The oleate solubility was explored in chloroform, hexane and toluene to prepare thin films of NCs using a dip coating process. From TEM images, the final structures show that increasing the solvent polarity improved self-assembly to prepare mono- and multi-layer superlattices, during solvent evaporation in a short time. The entangled organic chain in the NC surface offsets the limitations of the faceted NCs, improving the assembly quality, allowing the NC assembly to approach the formation of a hard sphere model, resulting in a FCC close-packed structure. Furthermore, the low interaction of chloroform with the capping layer reduces the shrinkage effect during the solvent evaporation preserving the array in the final self-assembled structure. Molecular dynamics simulations with soft potentials supported the conclusion that hexane interacts with the organic capping ligand, increasing the apparent radius of each NC and stabilizing the colloidal suspension, whereas chloroform is partially removed from the capping layer during the aggregation process, forming an array of nanoparticles.
- Published
- 2013
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