Ab initio study of high tridymite by the formalism generator coordinate Hartree-Fock

The Generator Coordinate Hartree-Fock (GCHF) Method is applied to generate extended 14s 8p and 17s 11p Gaussian basis sets for the atoms O and Si, respectively. The role of the weight functions in the assessment of the numerical integration range of the GCHF is shown. The Gaussian basis sets are contracted to [6s4p] O atom and [8s5p] Si atom by the Dunning's segmented contraction scheme. To evaluate the quality of our contracted [6s4p] and [8s5p] bases in molecular calculations we accomplish calculations of total and orbital energies in the Hartree-Fock-Roothaan method for O-2 and SiO molecules. We compare the results obtained with the our (14s 8p) and (17s 11p) bases sets with the of 6-311G basis and with values from the literature. The addition of one d polarization function in the silicon basis and its utilization with the basis for oxygen leads to the calculation of electronic properties and IR Spectrum of high tridymite in space group D-3d. (C) 1999 Elsevier B.V. B.V. All rights reserved.

Investigation of piezoelectricity in perovskite (LaFeO3): A theoretical study

In a previous report we studied theoretically the piezoelectric effect in barium titanate (BaTiO3) [O. Treu Filho, J.C. Pinheiro, R.T. Kondo, J. Mol. Struct. (THEOCHEM), 671 (2004) 71]. In this article we applied the Hartree-Fock (HF) theory in the investigation of piezoelectricity in LaFeO3. Initially, the generator coordinate HF (GCHF) method was used to build 22s14p, 30s19p13d, and 32s24p17d Gaussian basis sets for O(3p), Fe(D-5), and La(D-2) atoms. Then those basis sets were contracted to [7s6p], [13s8p6d], and [18s13p7d], respectively. The quality of the contracted basis sets in polyatomic calculations was evaluated through calculations of total and orbital energies (HOMO and HOMO-1) of (FeO1+)-Fe-2 and (LaO1+)-La-1. Finally, the contracted basis sets were supplemented with polarization and diffuse functions and used to investigate the piezoelectricity in LaFeO3. The calculated properties were dipole moment, total energy, and atomic charges and the analysis of those properties showed that covalent bonds constitute the electronic structure of [LaFCO3](2) fragment. Therefore, it is reasonable to believe that LaFeO3 does not present piezoelectric properties. (C) 2006 Elsevier B.V. All rights reserved.

Quantum chemical modeling of perovskite: An investigation of piezoelectricity in ferrite of yttrium

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Quantum mechanical study of YTiO3 to the investigation of piezoelectricity

In previous articles we reported through theoretical studies the piezoelectric effect in BaTiO3, SmTiO3, and YFeO3. In this paper, we used the Douglas-Kroll-Hess (DKH) second-order scalar relativistic method to investigate the piezoelectricity in YTiO3. In the calculations we used the [6s4p] and [10s5p4d] Gaussian basis sets for the O (3P) and Ti (5S) atoms, respectively, from the literature in combination with the (30s21p16d)/[15s9p6d] basis set for the Y ( 3D) atom, obtained by generator coordinate Hartree-Fock (GCHF) method, and they had their quality evaluated using calculations of total energy and orbital energies (HOMO and HOMO-1) of the 2TiO+1 and 1YO+1 fragments. The dipole moment, the total energy, and the total atomic charges in YTiO3 in C s space group were calculated. When we analyze those properties we verify that it is reasonable to believe that YTiO3 does not present piezoelectric properties. Copyright © 2011 Raimundo Dirceu de Paula Ferreira et al.

Fully Relativistic 4-Components DFT Investigation on Bonding and Dissociation Energy of HgO

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

POSITRON-HELIUM SCATTERING IN THE CLOSE-COUPLING APPROACH

We present results for low-energy elastic S-, P-, and D-wave phase shifts, capture and total cross sections of positron-helium scattering with different basis sets in the close coupling approach using realistic wave functions for He(1s1s), He(1s2(1)s), He(1s2(1)p) and positronium (1s) states. A resonance is found in the S-wave capture cross section at 84 eV.

In silico infrared and Raman spectroscopy under pressure: The case of CaSnO3 perovskite

The CaSnO3 perovskite is investigated under geochemical pressure, up to 25 GPa, by means of periodic ab initio calculations performed at B3LYP level with local Gaussian-type orbital basis sets. Structural, elastic, and spectroscopic (phonon wave-numbers, infrared and Raman intensities) properties are fully characterized and discussed. The evolution of the Raman spectrum of CaSnO3 under pressure is reported to remarkably agree with a recent experimental determination [J. Kung, Y. J. Lin, and C. M. Lin, J. Chem. Phys. 135, 224507 (2011)] as regards both wave-number shifts and intensity changes. All phonon modes are symmetry-labeled and bands assigned. The single-crystal total spectrum is symmetry-decomposed into the six directional spectra related to the components of the polarizability tensor. The infrared spectrum at increasing pressure is reported for the first time and its main features discussed. All calculations are performed using the CRYSTAL14 program, taking advantage of the new implementation of analytical infrared and Raman intensities for crystalline materials. (C) 2015 AIP Publishing LLC.

Theoretical study of the structure and stability of NbxOy, and NbxOy+ (x = 1-3; y = 2-5, 7, 8) clusters

Geometric, thermodynamic and electronic properties of cluster neutrals NbxOy and cations NbxOy+ (x = 1-3; y = 2-5, 7, 8) have been characterized theoretically. A DFT calculation using a hybrid combination of B3LYP with contracted Huzinaga basis sets. Numerical results of the relative stabilities, ionization potentials and band gaps of different clusters are in agreement with experiment. Analysis of dissociation channels supports the more stable building blocks as formed by NbO2, NbO2+ NbO3 and NbO3+ stoichiometries. The net atomic charges suggest that oxygen donor molecules can interact more favorably on central niobium atoms of cluster cations, while the interaction with oxygen acceptor molecules is more favorable on the terminal oxygen atoms of neutral clusters. A topological analysis of the electron localization function gradient field indicates that the clusters may be described as having a strong ionic interaction between Nb and O atoms. Published by Elsevier B.V. B.V.

Combined (13)C NMR and DFT/GIAO studies of the polyketides Aurasperone A and Fonsecinone A

Structural characterization by NMR spectroscopy and DFT calculations was performed for two dimeric naptho-gamma-pyrones, the polyketides Aurasperone A and Fonsecinone A. Experimental data ((13)C NMR chemical shifts and interatomic geometries) were found to be in reasonable agreement with theoretical ones, obtained at B3LYP level for three different basis sets (6-31G/6-31G(d)/6-31G(d,p)). Additionally, the dipolar moments calculation allowed explaining the different solubility for these molecules. The (13)C NMR theoretical chemical shifts were calculated with the GIAO method and the solvent effects were taken into account by means of the PCM approximation. In this work, the DFT/GIAO methodology shows to be a reliable tool in the assignment of experimental NMR chemical shifts of similar molecules. (C) 2008 Wiley Periodicals, Inc. Int J Quantum Chem 108: 2408-2416, 2008.

Influence of the tool edge geometry on specific cutting energy at high-speed cutting

This paper presents specific cutting energy measurements as a function of the cutting speed and tool cutting edge geometry. The experimental work was carried out on a vertical CNC machining center with 7,500 rpm spindle rotation and 7.5 kW power. Hardened steels ASTM H13 (50 HRC) were machined at conventional cutting speed and high-speed cutting (HSC). TiN coated carbides with seven different geometries of chip breaker were applied on dry tests. A special milling tool holder with only one cutting edge was developed and the machining forces needed to calculate the specific cutting energy were recorded using a piezoelectric 4-component dynamometer. Workpiece roughness and chip formation process were also evaluated. The results showed that the specific cutting energy decreased 15.5% when cutting speed was increased up to 700%. An increase of 1 °in tool chip breaker chamfer angle lead to a reduction in the specific cutting energy about 13.7% and 28.6% when machining at HSC and conventional cutting speed respectively. Furthermore the workpiece roughness values evaluated in all test conditions were very low, closer to those of typical grinding operations (∼0.20 μm). Probable adiabatic shear occurred on chip segmentation at HSC Copyright © 2007 by ABCM.

Variação da estrutura da vegetação arbórea em uma toposseqüência num vale da Serra de Maracaju, Aquidauana, MS

Pós-graduação em Agronomia (Produção Vegetal) - FCAV

Boundary of the rauzy fractal sets in R x C generated by P(x)=x(4)-x(3)-x(2)-x-1

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Boundary of the rauzy fractal sets in ℝ×ℂgenerated by p(x) = x 4- x 3 - x 2 -x- 1

We study the boundary of the 3-dimensional Rauzy fractal ε ⊂ ℝ×ℂ generated by the polynomial P(x) Dx 4-x 3-x 2-x-1. The finite automaton characterizing the boundary of ε is given explicitly. As a consequence we prove that the set ε has 18 neighboors where 6 of them intersect the central tile ε in a point. Our construction shows that the boundary is generated by an iterated function system starting with 2 compact sets.

Energy expenditure during multiple sets of leg press and bench press

The purpose of this study was to quantify energy expenditure (EE) during multiple sets of leg press (LP) and bench press (BP) exercises in 10 males with at least 1 yr of resistance training (RT). The subjects underwent two sessions to determine 1 repetition maximum (1RM) on the BP and LP and one protocol consisting of a warm up and 4 sets for 10 repetitions at 70% 1RM with a 3-min rest period between sets for each exercise. Energy expenditure was calculated as the sum of oxygen uptake (aerobic component), EPOC, and lactate production (anaerobic component). There were no significant differences in EE between exercises for sets 1 to 4 and the total energy expended. However, statistical analysis revealed a significant difference (P<0.05) between exercises in RT economy (BP, 0.0206 ± 0.0044 kcal·kg-1 vs. LP, 0.0051 ± 0.0015 kcal·kg-1). Within exercise comparison showed set 4 was significantly different from sets 1 and 3 for BP, and for LP a significant difference was found between set 4 and sets 1, 2 and 3. Our results point to an increase in EE during multiple sets at 70% 1RM and show that in spite of the difference in muscle mass involved and total work done during each type of exercise, EE was not different due to greater economy during the LP.

Reduction capability of soil humic substances from the Rio Negro basin, Brazil, towards Hg(II) studied by a multimethod approach and principal component analysis (PCA)

This paper characterizes humic substances (HS) extracted from soil samples collected in the Rio Negro basin in the state of Amazonas, Brazil, particularly investigating their reduction capabilities towards Hg(II) in order to elucidate potential mercury cycling/volatilization in this environment. For this reason, a multimethod approach was used, consisting of both instrumental methods (elemental analysis, EPR, solid-state NMR, FIA combined with cold-vapor AAS of Hg(0)) and statistical methods such as principal component analysis (PCA) and a central composite factorial planning method. The HS under study were divided into groups, complexing and reducing ones, owing to different distribution of their functionalities. The main functionalities (cor)related with reduction of Hg(II) were phenolic, carboxylic and amide groups, while the groups related with complexation of Hg(II) were ethers, hydroxyls, aldehydes and ketones. The HS extracted from floodable regions of the Rio Negro basin presented a greater capacity to retain (to complex, to adsorb physically and/or chemically) Hg(II), while nonfloodable regions showed a greater capacity to reduce Hg(II), indicating that HS extracted from different types of regions contribute in different ways to the biogeochemical mercury cycle in the basin of the mid-Rio Negro, AM, Brazil. (c) 2007 Published by Elsevier B.V.