Density functional theory study on the structural and electronic properties of low index rutile surfaces for TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 composite systems

The present study is concerned with the structural and electronic properties of the TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 composite systems. Periodic quantum mechanical method with density functional theory at the B3LYP level has been carried out. Relaxed surface energies, structural characteristics and electronic properties of the (I 10), (0 10), (10 1) and (00) low-index rutile surfaces for TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 models are studied. For, comparison purposes, the bare rutile TiO2 and SnO2 structures are also analyzed and compared with previous theoretical and experimental data. The calculated surface energy for both rutile TiO2 and SnO2 surfaces follows the sequence (110) < (010) < (101) < (001) and the energy increases as (010) < (101) < (110) < (001) and (010) approximate to (110) < (101) < (001) for SnO2/TiO2/SnO2 and TiO2/SnO2/TiO2 composite systems, respectively. SnO2/TiO2/SnO2 presents larger values of surface energy than the individual SnO2 and TiO2 metal oxides and the TiO2/SnO2/TiO2 system renders surface energy values of the same order that the TiO2 and lower than the SnO2. An analysis of the electronic structure of the TiO2/SnO2/TiO2 and SnO2/TiO2/SnO2 systems shows that the main characteristics of the upper part of the valence bands for all the studied surfaces are dominated by the external layers, i.e., by the TiO2 and the SnO2, respectively, and the topology of the lower part of the conduction bands looks like the core layers. There is an energy stabilization of both valence band top and conduction band bottom for (110) and (010) surfaces of the SnO2/TiO2/SnO2 composite system in relation to their core TiO2, whereas an opposite trend is found for the same surfaces of the TiO2/SnO2/TiO2 composite system in relation to the bare SnO2. The present theoretical results may explain the growth of TiO2@SnO2 bimorph composite nanotape.

Shape controlled synthesis of CaMoO4 thin films and their photoluminescence property

CaMoO4 (CMO) disordered and ordered thin films were prepared by the complex polymerization method (CPM). The films were annealed at different temperatures and time in a conventional resistive furnace (RF) and in a microwave (MW) oven. The microstructure and surface morphology of the structure were monitored by atomic force microscopy (AFM) and high-resolution scanning electron microscopy (HRSEM). Order and disorder were characterized by X-ray diffraction (XRD) and optical reflectance. A strong photoluminescence (PL) emission was observed in the disordered thin films and was attributed to complex cluster vacancies. The experimental results were compared with density functional and Hartree-Fock calculations. (C) 2008 Elsevier B.V. All rights reserved.

Single walled MgF2 nanotubes

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

First principles calculations on the origin of violet-blue and green light photoluminescence emission in SrZrO3 and SrTiO3 perovskites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Structural and vibrational study of cubic Sb2O3 under high pressure

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

C - H ⋯ 0 and N - H ⋯ 0 hydrogen bonds in liquid amides investigated by monte carlo simulation

Monte Carlo simulations of liquid formamide, N-methylformamide (MF), and N, N-dimethytformamide (DMF) have been performed in the isothermal and isobaric ensemble at 298 K and 1 atm, aiming to investigate the C-H ⋯ O and N-H ⋯ O hydrogen bonds. The interaction energy was calculated using the classical 6-12 Lennard-Jones pairwise potential plus a Coulomb term on a rigid six-site molecular model with the potential parameters being optimized in this work. Theoretical values obtained for heat of vaporization and liquid densities are in good agreement with the experimental data. The radial distribution function [RDF, g(r)] obtained compare well with R-X diffraction data available. The RDF and molecular mechanics (MM2) minimization show that the C-H ⋯ O interaction has a significant role in the structure of the three liquids. These results are supported by ab initio calculations. This interaction is particularly important in the structure of MF. The intensity of the N - H ⋯ O hydrogen bond is greater in the MF than formamide. This could explain some anomalous properties verified in MF. © 1997 John Wiley & Sons, Inc.

Orphan nuclear receptor NGFI-B forms dimers with nonclassical interface

The orphan receptor nerve growth factor-induced B (NGFI-B) is a member of the nuclear receptor's subfamily 4A (Nr4a). NGFI-B was shown to be capable of binding both as a monomer to an extended half-site containing a single AAAGGTCA motif and also as a homodimer to a widely separated everted repeat, as opposed to a large number of nuclear receptors that recognize and bind specific DNA sequences predominantly as homo- and/or heterodimers. To unveil the structural organization of NGFI-B in solution, we determined the quaternary structure of the NGFI-B LBD by a combination of ab initio procedures from small-angle X-ray scattering (SAXS) data and hydrogen-deuterium exchange followed by mass spectrometry. Here we report that the protein forms dimers in solution with a radius of gyration of 2.9 nm and maximum dimension of 9.0 nm. We also show that the NGFI-B LBD dimer is V-shaped, with the opening angle significantly larger than that of classical dimer's exemplified by estrogen receptor (ER) or retinoid X receptor (RXR). Surprisingly, NGFI-B dimers formation does not occur via the classical nuclear receptor dimerization interface exemplified by ER and RXR, but instead, involves an extended surface area composed of the loop between helices 3 and 4 and C-terminal fraction of the helix 3. Remarkably, the NGFI-B dimer interface is similar to the dimerization interface earlier revealed for glucocorticoid nuclear receptor (GR), which might be relevant to the recognition of cognate DNA response elements by NGFI-B and to antagonism of NGFI-B-dependent transcription exercised by GR in cells. Published by Cold Spring Harbor Laboratory Press. Copyright © 2007 The Protein Society.

Temperature dependence of structural and electronic properties of the spin-liquid candidate κ-(BEDT-TTF) 2Cu 2(CN) 3

We investigate the effect that the temperature dependence of the crystal structure of a two-dimensional organic charge-transfer salt has on the low-energy Hamiltonian representation of the electronic structure. For that, we determine the crystal structure of κ-(BEDT-TTF) 2Cu 2(CN) 3 for a series of temperatures between T=5 and 300 K by single crystal X-ray diffraction and analyze the evolution of the electronic structure with temperature by using density functional theory and tight binding methods. We find a considerable temperature dependence of the corresponding triangular lattice Hubbard Hamiltonian parameters. We conclude that even in the absence of a change of symmetry, the temperature dependence of quantities like frustration and interaction strength can be significant and should be taken into account. © 2012 American Physical Society.

Quantum mechanical modeling of excited electronic states and their relationship to cathodoluminescence of BaZrO3

First-principles calculations set the comprehension over performance of novel cathodoluminescence (CL) properties of BaZrO3 prepared through microwave-assisted hydrothermal. Ground (singlet, s*) and excited (singlet s** and triplet t**) electronic states were built from zirconium displacement of 0.2 Å in {001} direction. Each ground and excited states were characterized by the correlation of their corresponding geometry with electronic structures and Raman vibrational frequencies which were also identified experimentally. A kind of optical polarization switching was identified by the redistribution of 4dz2 and 4dxz (Zr) orbitals and 2pz O orbital. As a consequence, asymmetric bending and stretching modes theoretically obtained reveal a direct dependence with their polyhedral intracluster and/or extracluster ZrO6 distortions with electronic structure. Then, CL of the as-synthesized BaZrO3 can be interpreted as a result of stable triplet excited states, which are able to trap electrons, delaying the emission process due to spin multiplicity changes. © 2013 AIP Publishing LLC.

Métodos periódicos aplicados à determinação e análise de propriedades eletrônicas e elásticas em peroviskitas do tipo BaZrO.3 e BaTiO.3

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Cálculos de estrutura eletrônica de materiais mediante combinação linear de orbitais atômicos

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Propriedades ferroelétricas, microestruturais e ópticas dos materiais cerâmicos Ba0,5 Sr0,5 (Ti1-ySny) O3

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Métodos teóricos na investigação da estrutura eletrônica do resveratrol e derivados

Na apresentação do desenvolvimento desta tese foram utilizados métodos ab initio, semiempíricos, e teoria do funcional densidade na investigação das propriedades do estado fundamental e estados excitados do Resveratrol e estruturas moleculares similares, assim como suas propriedades espectroscópicas. O Resveratrol é uma fitoalexina com propriedades antioxidantes, que tem como estruturas derivadas semelhantes, a Piceatannol, Para-vinylphenylphenol e Resveratrol-dihydroxyl_N (N=1,2 e 3). Os resultados obtidos correspondem à análise dos parâmetros moleculares e propriedades eletrônicas; as simulações dos espectros que correspondem as fotoexcitações para cada uma das moléculas foram feitos através de pacotes computacionais. Os métodos aproximativos utilizados nos cálculos comprovam os resultados obtidos experimentalmente, de forma a contribuir como um indicador às prováveis modificações nas propriedades químicas, físicas e biológicas do Resveratrol.

Transporte eletrônico e quiralidade molecular: um estudo de dispositivos orgânicos em sistemas de dois terminais

No presente trabalho, investigamos o transporte eletrônico molecular em dois compostos orgânicos, o Ponceau SS (PSS) e o Oligo-(para)fenileno-vinileno (PPV) através de cálculos ab initio e função de Green de não equilíbrio (FGNE). Estes métodos demonstraram equivalência para a descrição destes dispositivos moleculares. Fizemos cálculos quânticos para o Hamiltoniano derivado de Hartree-Fock (HF) e obtivemos as propriedades de corrente-voltagem (I-V) para as duas estruturas moleculares. Com o método FGNE conseguimos modelar o transporte através de um sistema de multiníveis eletrônicos obtendo a corrente descrevendo as regiões de ressonância e a assimetria do sistema. Como resposta o PSS demonstrou assimetria para polarizações direta e reversa e a ressonância é alcançada mostrando que o dispositivo opere como um transistor molecular bi-direcional. Para o PPV investigamos também as propriedades geométricas através da conexão entre transporte eletrônico e o grau de quiralidade molecular que foi calculado usando o índice quiral que depende apenas das posições atômicas. Obtivemos que moléculas quirais e propriedades estruturais podem induzir uma assimetria no transporte eletrônico, resultando num processo de retificação. Também obtivemos que a resposta elétrica (I-V) e momento de dipolo elétrico são proporcionais ao grau de quiralidade molecular. Estes resultados sugerem que o transporte eletrônico neste sistema pode ser explorado na avaliação do seu grau de quiralidade.

Dicroísmo circular vibracional e eletrônico na determinação da configuração absoluta de benzopiranos de Peperomia obtusifolia e Piper gaudichaudianum (Piperaceae): implicações biológicas e biossintéticas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)