Development of basis sets to calculations of the electronic structure of YMnO3

The generator coordinate Hartree-Fock method was used to develop 20s17p, 30s20p14d, and 30s21p16d Gaussian basis sets for the O ((3)p), Mn (S-6), and Y (D-2) atoms, respectively. The Gaussian basis sets were contracted to 20s17p/9s7p, 30s20p14d/11s7p7d, and 30s21p16d/14s7p7d and utilized in calculations of total energy and orbital energies of the (MnO1+)-Mn-5 and (YO1+)-Y-3 fragments to evaluate its quality in molecular studies. Finally, the contracted basis set for O atom was supplemented with one polarization function of d symmetry and used along with the other contracted basis sets (for Mn and Y) to calculate dipole moments, total energy, and total atomic charges in YMnO3 in space group D-6h. The analysis of those properties showed that is reasonable to believe that YMnO3 present behavior of piezoelectric material. (C) 2003 Elsevier B.V. All rights reserved.

Ab Initio correlated all electron dirac-fock calculations for Eka-Francium Fluoride (E119F)

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

Electrochemistry of organometallic compounds. Part III. Oxidations of methyl derivatives of organocobalt(III) complexes with delocalized electronic structure in dimethylformamide

The influence of the equatorial ligand on the electrochemical oxidation of the compounds [H3CCo(chel)B], where chel is bis (dimethylglyoximato), (DH)2; bis(salicylaldehyde)ethylenediimine, salen; bis(salicylaldehyde) o-phenylenediimine, salophen; bis(salicylaldehyde)cyclohexylenediimine, salcn; bis(acetylacetone) ethylenediimine, bae; and where B is pyridine when chel is (DH2), and dimethylformamide (DMF) when chel represents a Schiff base (salen, salcn, salophen and bae), was studied by means of cyclic voltammetry in DMF, 0.2 M in tetraethylammonium perchlorate, between 25 and -25°C, with a platinum disk working electrode. Absorption spectra in the visible and near ultraviolet regions for these compounds in DMF at 25°C were obtained. The complexes exhibit a reversible one-electron oxidation, at -20°C with scan rates >0.5 V s-; chemical reactions following electron transfer are not detected under these conditions. At slower potential or higher temperatures, the oxidized product decomposes chemically in a solvent-assisted (or nucleophile-assisted) reaction, yielding products which are electroactive in the applied potential range. The behavior of the [H3CCo (DH2)py] derivative is better described as a quasi-reversible charge transfer followed by an irreversible chemical reaction. Experimental evidence suggests that in the case of the [H3CCo(bae)] derivative at -20°C, the reactive -species is pentacoordinated and weakly adsorbed at the electrode surface. The value of E 1 2 and the energies of the first two absorption bands in the visible spectra reveal the ability of the studied complexes to donate and to delocalize electronic charge. © 1982.

Electronic structure of polyacetylene with bonded oxygen

In this work we have studied the electronic structure of finite polyacetylene chains with structural oxygen-bonding models following data from 13C-NMR experiments. We have used a combination of Austin Method One and Hydrogenic Atoms in Molecules version 3 methods to perform geometric and spectroscopic calculations. Our results show that the electronically-active states are generally unaffected by the incorporation of oxygen. © 1992.

Theoretical investigation of the electronic structure and absorption spectra of carbon cluster nanotubes

Electronic and optical properties of recently discovered single-shell carbon cluster nanotubes are studied through a semiempirical INDOCI method. The calculations are performed within the cluster model and include up to 196 atoms. The trend of the forbidden band gap with the number of carbon atoms (Cn n = 60, 10, 140) for a fixed diameter is analyzed. With increasing n the band gap decreases, as expected. The tubule, with diameter of 7.2Å (as C60-Buckyball) is predicted to be a metal or a narrow-gap semiconductor. The calculated absorption spectra of the clusters show a characteristic strong peak around 40,000 cm-1. Other features of the calculated UV-visible absorption spectra are discussed. © 1994.

Crystal, Molecular, and Electronic Structure of 1-Acetyl-indoline and Derivatives

The crystal and molecular structures of the following molecules have been determined: 1-acetyl-indoline, 1-acetyl-5-nitro-indoline, 1-acetyl-5-nitro-7-bromo-indoline, 1-acetyl-5-bromo-7-nitro-indoline, and 1-acetyl-5-bromo-7-nitro-indol. Molecular orbital calculations are performed for these compounds and two related species.

Density functional theory calculation of the electronic structure of Ba0.5Sr0.5TiO3: Photoluminescent properties and structural disorder

First-principles quantum-mechanical techniques, based on density functional theory (B3LYP level) were employed to study the electronic structure of ordered and deformed asymmetric models for Ba0.5Sr 0.5TiO3. Electronic properties are analyzed and the relevance of the present theoretical and experimental results on the photoluminescence behavior is discussed. The presence of localized electronic levels in the band gap, due to the symmetry break, would be responsible for the visible photoluminescence of the amorphous state at room temperature. Thin films were synthesized following a soft chemical processing. Their structure was confirmed by x-ray data and the corresponding photoluminescence properties measured.

Electronic structure and magnetic properties of FeWO 4 nanocrystals synthesized by the microwave-hydrothermal method

This communication reports that FeWO 4 nanocrystals were successfully synthesized by the microwave-hydrothermal method at 443 K for 1 h. The structure and shape of these nanocrystals were characterized by X-ray diffraction, Rietveld refinement, and transmission electron microscopy. The experimental results and first principles calculations were combined to explain the electronic structure and magnetic properties. Experimental data were obtained by magnetization measurements for different applied magnetic fields. Theoretical calculations revealed that magnetic properties of FeWO 4 nanocrystals can be assigned to two magnetic orderings with parallel or antiparallel spins in adjacent chains. These factors are crucial to understanding of competition between ferro- and antiferromagnetic behavior. © 2012 Elsevier Inc.

A combined theoretical and experimental study of electronic structure and optical properties of β-ZnMoO4 microcrystals

In this paper, a combined theoretical and experimental study on the electronic structure and photoluminescence (PL) properties of beta zinc molybdate (β-ZnMoO4) microcrystals synthesized by the hydrothermal method has been employed. These crystals were structurally characterized by X-ray diffraction (XRD), Rietveld refinement, Fourier transform Raman (FT-Raman) and Fourier transform infrared (FT-IR) spectroscopies. Their optical properties were investigated by ultraviolet-visible (UV-Vis) absorption spectroscopy and PL measurements. First-principles quantum mechanical calculations based on the density functional theory at the B3LYP level have been carried out. XRD patterns, Rietveld refinement, FT-Raman and FT-IR spectra showed that these crystals have a wolframite-type monoclinic structure. The Raman and IR frequencies experimental results are in reasonable agreement with theoretically calculated results. UV-Vis absorption measurements shows an optical band gap value of 3.17 eV, while the calculated band structure has a value of 3.22 eV. The density of states indicate that the main orbitals involved in the electronic structure of β-ZnMoO4 crystals are (O 2p-valence band and Mo 4d-conduction band). Finally, PL properties of β-ZnMoO4 crystals are explained by means of distortions effects in octahedral [ZnO6] and [MoO6] clusters and inhomogeneous electronic distribution into the lattice with the electron density map. © 2013 Elsevier Ltd. All rights reserved.

Effect of chemical modifications on the electronic structure of poly(3-hexylthiophene)

The widespread use of poly(3-hexylthiophene) (P3HT) in the active layers of organic solar cells indicates that it possesses chemical stability and solubility suitable for such an application. However, it would be desirable to have a material that can maintain these properties but with a smaller bandgap, which would lead to more efficient energy harvesting of the solar spectrum. Fifteen P3HT derivatives were studied using the Density Functional Theory. The conclusion is that it is possible to obtain compounds with significantly smaller bandgaps and with solubility and stability similar to that of P3HT, mostly through the binding of oxygen atoms or conjugated organic groups to the thiophenic ring. © 2013 Wiley Periodicals, Inc.

Local electronic structure, optical bandgap and photoluminescence (PL) properties of Ba(Zr0.75Ti0.25)O3 powders

Ba(Zr0.75Ti0.25)O3 (BZT-75/25) powders were synthesized by the polymeric precursor method. Samples were structurally characterized by X-ray diffraction (XRD), Rietveld refinement, X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) techniques. Their electronic structures were evaluated by first-principle quantum mechanical calculations based on density functional theory at the B3LYP level. Their optical properties were investigated by ultraviolet-visible (UV-Vis) spectroscopy and photoluminescence (PL) measurements at room temperature. XRD patterns and Rietveld refinement data indicate that the samples have a cubic structure. XANES spectra confirm the presence of pyramidal [TiO5] clusters and octahedral [TiO6] clusters in the disordered BZT-75/25 powders. EXAFS spectra indicate distortion of Ti-O and Ti-O-Ti bonds the first and second coordination shells, respectively. UV-Vis absorption spectra confirm the presence of different optical bandgap values and the band structure indicates an indirect bandgap for this material. The density of states demonstrates that intermediate energy levels occur between the valence band (VB) and the conduction band (CB). These electronic levels are due to the predominance of 4d orbitals of Zr atoms in relation to 3d orbitals of Ti atoms in the CB, while the VB is dominated by 2p orbitals related to O atoms. There was good correlation between the experimental and theoretical optical bandgap values. When excited at 482 nm at room temperature, BZT-75/25 powder treated at 500 C for 2 h exhibited broad and intense PL emission with a maximum at 578 nm in the yellow region. © 2013 Elsevier Ltd. All rights reserved.

The correlation between electronic structure and antimalarial activity of alkoxylated and hydroxylated chalcones

Chalcones have shown potential to several pharmacological applications including antimalarial properties. We employed multivariate data analysis to correlate the antimalarial activity with electronic structure descriptors obtained through quantum mechanical calculations. The results show high statistical significance and bring valuable insights in order to design new compounds. © 2013 Springer Science+Business Media New York.

Ab Initio correlated all electron Dirac-Fock calculations for eka-francium fluoride (E119F)

Resultados obtidos por cálculos Dirac-Fock correlacionados de 4 componentes para o fluoreto do elemento E119 (Eka-Frâncio) com base estável e precisa, livre de prolapso variacional, são reportados neste trabalho. No nível CCSD(T), a distância de equilíbrio R_e, frequência harmônica ω_e e energia de dissociação D_e são 2,432 Å, 354,97 cm_-1 e 116,92 kcal mol_-1, respectivamente. Também são reportados base livre de prolapso variacional de 4 componentes para o elemento 119, uma curva analítica de energia potencial precisa e o espectro vibracional a partir dos dados obtidos no nível CCSD(T). Nossos resultados sugerem que a molécula E119F deva ser menos iônica que seus fluoretos alcalinos homólogos mais leves, em contraste com o senso químico comum baseado nas propriedades periódicas - era de se esperar nesta molécula a ligação química mais iônica possível. Também encontramos que a correção do tipo modelo de carga para negligenciar as integrais do tipo SS resulta em erros insignificantes e acelera os cálculos cerca de 3 vezes no nível CCSD(T) e cerca de 4 vezes no nível DFT/B3LYP.

Analysis of electronic structure of boron nitride nanotubes with different positions of intrinsic impurities

The pristine boron nitride nanotubes have a large direct band gap around 5 eV. This band gap can be engineered by doping. We investigate electronic structure of the doped hexagonal boron nitride (5,5) nanotubes using the linearized augmented cylindrical wave method. In particular, this work focuses on systematical study of the band gap and the density of states around the Fermi-level when the nanotubes are doped by intrinsic impurities of two substitutional boron atoms in a super cell and a comparative analysis of the relative stability of three structures studied here. This corresponds to 3.3% of impurity concentration. We calculate 29 configurations of the nanotubes with different positions of the intrinsic impurities in the nanotube. The band gap and density of states around the Fermi level show strong dependence on the relative positions of the impurity atoms. The two defect sub bands called D^∏(B) appear in the band gap of the pristine nanotube. The doped nanotubes possess p-type semiconductor properties with the band gap of 1.3-1.9 eV.

Experimental and Theoretical Investigations of Electronic Structure and Photoluminescence Properties of beta-Ag2MoO4 Microcrystals

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)