Analysis of the structural and electronic properties of 1-(5-Hydroxymethyl - 4 -[ 5 - (5-oxo-5-piperidin-1-yl-penta-1,3dienyl)-benzo[1,3]dioxol-2-yl] -tetrahydro-furan-2-yl)-5-methyl-1H-pyrimidine-2,4dione molecule

The structural and electronic properties of 1-(5-Hydroxymethyl - 4 -[ 5 - (5-oxo-5-piperidin- 1 -yl-penta- 1,3 -dienyl)-benzo [1,3] dioxol- 2 -yl]-tetrahydro -furan-2 -yl)-5-methy l-1Hpyrimidine-2,4dione (AHE) molecule have been investigated theoretically by performing density functional theory (DFT), and semi empirical molecular orbital calculations. The geometry of the molecule is optimized at the level of Austin Model 1 (AM1), and the electronic properties and relative energies of the molecules have been calculated by density functional theory in the ground state. The resultant dipole moment of the AHE molecule is about 2.6 and 2.3 Debyes by AM1 and DFT methods respectively, This property of AHE makes it an active molecule with its environment, that is AHE molecule may interacts with its environment strongly in solution.

Structural and Electronic Properties of Dipyridamole and Derivatives

Quantum mechanical calculations at the B3LYP theory level, together with the 6-31G* basis set, were employed to obtain the energy, ionization potential, and polarizabilites for dipyridamole and derivatives, which are compared with their biological activity. Density functional calculations of the spin densities were performed for radical formed by electron abstraction of dipyridamole and derivatives. The unpaired electron remains in dipyridamole is localized on the nitrogen atoms in the substituent positions 1, 3, 5, 7, 11, 12, 13, 14, with participation of the 9 and 10 carbons in the pyrimido-pyrimidine ring. The antioxidant activity is related with ionization potential, polarizability and Log P.

Periodic study on the structural and electronic properties of bulk, oxidized and reduced SnO2(110) surfaces and the interaction with O-2

The structural and electronic properties of bulk and both oxidized and reduced SnO2(110) surfaces as well as the adsorption process of O-2 on the reduced surface have been investigated by periodic DFT calculations at B3LYP level. The lattice parameters, charge distribution, density of states and band structure are reported for the bulk and surfaces. Surface relaxation effects have been explicitly taken into account by optimizing slab models of nine and seven atomic layers representing the oxidized and reduced surfaces, respectively. The conductivity behavior of the reduced SnO2(110) surface is explained by a distribution of the electrons in the electronic states in the band gap induced by oxygen vacancies. Three types of adsorption approaches of O-2 on the four-fold tin at the reduced SuO(2)(110) surface have been considered. The most exothermic channel corresponds to the adsorption of O-2 parallel to the surface and to the four-fold tin row, and it is believed to be associated with the formation of a peroxo O-2(2-) species. The chemisorption of O-2 on reduced SnO2(110) surface causes a significant depopulation of states along the band gap and it is shown to trap the electrons in the chemisorbed complex producing an electron-depleted space-charge layer in the inner surface region of the material in agreement with some experimental evidences. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Structural and electronic properties of PbTiO3 slabs: a DFT periodic study

Structural and electronic properties of the bulk and relaxed surfaces (TiO2 and PbO terminated) of cubic PbTiO3 are investigated by means of periodic quantum-mechanical calculations based on density functional theory. It is observed that the difference in surface energies is small and relaxations effects are most prominent for Ti and Ph surface atoms. The electronic structure shows a splitting of the lowest conduction bands for the TiO2 terminated surface and of the highest valence bands for the PbO terminated slab. The calculated indirect band gap is: 3.18, 2.99 and 3.03 eV for bulk, TiO2 and PbO terminations, respectively. The electron density maps show that the Ti-O bond has a partial covalent character, whereas the Pb-O bonds present a very low covalency. (C) 2004 Elsevier B.V. All rights reserved.

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.

Structural and Electronic Properties of Lithiated SnO2. A Periodic DFT Study

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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.

A DFT Study of Structural and Electronic Properties of ZnS Polymorphs and its Pressure-Induced Phase Transitions

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

The Structural and Electronic Properties of Tin Oxide Nanowires: An Ab Initio Investigation

We performed an ab initio investigation on the properties of rutile tin oxide (SnOx) nanowires. We computed the wire properties determining the equilibrium geometries, binding energies, and electronic band structures for several wire dimensions and surface facet configurations. The results allowed us to establish scaling laws for the structural properties, in terms of the nanowire perimeters. The results also showed that the surface states control most of the electronic properties of the nanowires. Oxygen incorporation in the nanowire surfaces passivated the surface-related electronic states, and the resulting quantum properties and scaling laws were fully consistent with electrons confined inside the nanowire. Additionally, oxygen incorporation in the wire surfaces generated an unbalanced concentration of spin up and down electrons, leading to magnetic states for the nanowires.

Manipulating the structural and electronic properties of epitaxial NaNbO3 films via strain and stoichiometry

Due to their intriguing dielectric, pyroelectric, elasto-electric, or opto-electric properties, oxide ferroelectrics are vital candidates for the fabrication of most electronics. However, these extraordinary properties exist mainly in the temperature regime around the ferroelectric phase transition, which is usually several hundreds of K away from room temperature. Therefore, the manipulation of oxide ferroelectrics, especially moving the ferroelectric transition towards room temperature, is of great interest for application and also basic research. In this thesis, we demonstrate this using examples of NaNbO3 films. We show that the transition temperature of these films can be modified via plastic strain caused by epitaxial film growth on a structurally mismatched substrate, and this strain can be fixed by controlling the stoichiometry. The structural and electronic properties of Na1+xNbO3+δ thin films are carefully examined by among others XRD (e.g. RSM) and TEM and cryoelectronic measurements. Especially the electronic features are carefully analyzed via specially developed interdigitated electrodes in combination with integrated temperature sensor and heater. The electronic data are interpreted using existing as well as novel theories and models, they are proved to be closely correlated to the structural characteristics. The major results are: -Na1+xNbO3+δ thin films can be grown epitaxially on (110)NdGaO3 with a thickness up to 140 nm (thicker films have not been studied). Plastic relaxation of the compressive strain sets in when the thickness of the film exceeds approximately 10 – 15 nm. Films with excess Na are mainly composed of NaNbO3 with minor contribution of Na3NbO4. The latter phase seems to form nanoprecipitates that are homogeneously distributed in the NaNbO3 film which helps to stabilize the film and reduce the relaxation of the strain. -For the nominally stoichiometric films, the compressive strain leads to a broad and frequency-dispersive phase transition at lower temperature (125 – 147 K). This could be either a new transition or a shift in temperature of a known transition. Considering the broadness and frequency dispersion of the transition, this is actually a transition from the dielectric state at high temperature to a relaxor-type ferroelectric state at low temperature. The latter is based on the formation of polar nano-regions (PNRs). Using the electric field dependence of the freezing temperature, allows a direct estimation of the volume (70 to 270 nm3) and diameter (5.2 to 8 nm, spherical approximation) of the PNRs. The values confirm with literature values which were measured by other technologies. -In case of the off-stoichiometric samples, we observe again the classical ferroelectric behavior. However, the thermally hysteretic phase transition which is observed around 620 – 660 K for unstrained material is shifted to room temperature due to the compressive strain. Beside to the temperature shift, the temperature dependence of the permittivity is nearly identical for strained and unstrained materials. -The last but not least, in all cases, a significant anisotropy in the electronic and structural properties is observed which arises automatically from the anisotropic strain caused by the orthorhombic structure of the substrate. However, this anisotropy cannot be explained by the classical model which tries to fit an orthorhombic film onto an orthorhombic substrate. A novel “square lattice” model in which the films adapt a “square” shaped lattice in the plane of the film during the epitaxial growth at elevated temperature (~1000 K) nicely explains the experimental results. In this thesis we sketch a way to manipulate the ferroelectricity of NaNbO3 films via strain and stoichiometry. The results indicate that compressive strain which is generated by the epitaxial growth of the film on mismatched substrate is able to reduce the ferroelectric transition temperature or induce a phase transition at low temperature. Moreover, by adding Na in the NaNbO3 film a secondary phase Na3NbO4 is formed which seems to stabilize the main phase NaNbO3 and the strain and, thus, is able to engineer the ferroelectric behavior from the expected classical ferroelectric for perfect stoichiometry to relaxor-type ferroelectric for slightly off-stoichiometry, back to classical ferroelectric for larger off-stoichiometry. Both strain and stoichiometry are proven as perfect methods to optimize the ferroelectric properties of oxide films.

First-Principles Study of Pressure-Induced Phase Transitions and Electronic Properties of Ag2MoO4

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A theoretical investigation of the structural and eletronic properties of orthorhombic CaZrO3

A CaZrO3 (CZO) powder was prepared by the soft chemical, polymeric precursor method (PPM). The CZO crystalline structure was investigated by powder X-ray diffraction (XDR), Retvield Refinament data, Raman spectra and ultraviolet–visible absorption spectroscopy. A theoretical study was performed using a periodic quantum mechanical calculation (CRYSTAL09 program). The periodic model built for the crystalline CZO structure was consistent with the experimental data obtained from structural and electronic properties. These results show that the material has an orthorhombic structure with experimental and theoretical gap values of 5.7 eV and 6.2 eV, respectively. In this article, we discuss the hybridization process of the oxygen p-orbitals and of the zirconium d-orbitals and analyze their band structures and density of states (partial and total).

The correlation of structure and electronic properties near the surface of transition metal oxides

The strong couplings between different degrees of freedom are believed to be responsible for novel and complex phenomena discovered in transition metal oxides (TMOs). The physical complexity is directly responsible for their tunability. Creating surfaces/interfaces add an additional ' man-made' twist, approaching the quantum phenomena of correlated materials. ^ The dissertation focused on the structural and electronic properties in proximity of surface of three prototype TMO compounds by using three complementary techniques: scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and low energy electron diffraction, particularly emphasized the effects of broken symmetry and imperfections like defects on the coupling between charge and lattice degrees of freedom. ^ Ca1.5Sr0.5RuO4 is a layered ruthenate with square lattice and at the boundary of magnetic/orbital instability in Ca2-xSrxRuO4. That the substitution of Sr 2+ with Ca2+ causing RuO6 rotation narrows the dxy band width and changes the Fermi surface topology. Particularly, the γ(dxy) Fermi surface sheet exhibited hole-like in Ca1.5Sr0.5RuO4 in contrast to electron-like in Sr2RuO4, showing a strong charge-lattice coupling. ^ Na0.75CoO2 is a layered cobaltite with triangular lattice exhibiting extraordinary thermoelectric properties. The well-ordered CoO2-terminated surface with random Na distribution was observed. However, lattice constants of the surface are smaller than that in bulk. The surface density of states (DOS) showed strong temperature dependence. Especially, an unusual shift of the minimum DOS occurs below 230 K, clearly indicating a local charging effect on the surface. ^ Cd2Re2O7 is the first known pyrochlore oxide superconductor (Tc ∼ 1K). It exhibited an unusual second-order phase transition occurring at TS1 = 200 K and a controversial first-order transition at TS2 = 120 K. While bulk properties display large anomalies at TS1 but rather subtle and sample-dependent changes at TS2, the surface DOS near the EF show no change at T s1 but a substantial increase below TS2---a complete reversal as the signature for the transitions. We argued that crystal imperfections, mainly defects, which were considerably enhanced at the surface, resulted in the transition at TS2. ^