Luiz N. Oliveira

Density functionals not based on the electron gas: local-density approximation for a Luttinger liquid.

By shifting the reference system for the local-density approximation (LDA) from the electron gas to other model systems, one obtains a new class of density functionals, which by design account for the correlations present in the chosen reference system. This strategy is illustrated by constructing an explicit LDA for the one-dimensional Hubbard model. While the traditional ab initio LDA is based on a Fermi liquid (the three-dimensional interacting electron gas), this one is based on a Luttinger liquid. First applications to inhomogeneous Hubbard models, including one containing a localized impurity, are reported.

Transport of excess charge in electron‐irradiated dielectrics

Irradiation of dielectrics with nonpenetrating electron beams has been used for practical purposes, e.g., manufacturing of electrets, and as a research tool, e.g., the investigation of induced conductivity and transport properties. The present paper develops some aspects of the theory of charge transport and storage and radiation‐induced conductivity in irradiated dielectrics. It is assumed that the dielectric is kept in short circuit and that the range of the incident electron beam is smaller than half the sample thickness. The treatment applies only to dielectrics which have a very low dark conductivity and contain a great number of deep traps.

A Known SOST Gene Mutation Causes Sclerosteosis in a Familial and an Isolated Case from Brazilian Origin

Sclerosteosis is a severe, rare, autosomal recessive bone condition that is characterized by a progressive craniotubular hyperostosis. The main features are a significant sclerosis of the long bones, ribs, pelvis, and skull, leading to facial distortion and entrapment of cranial nerves. Clinical features include a tall stature, nail dysplasia, cutaneous syndactyly of some fingers, and raised intracranial pressure. The sclerosteosis gene has been mapped to chromosome 17q12-21 and is currently known as the SOST gene encoding the sclerostin protein. Here, we report on one familial and one isolated case of Brazilian origin with the clinical and molecular diagnosis of sclerosteosis. The radiological and clinical features are described, and the diagnosis of sclerosteosis was confirmed in both cases by mutation analysis of the SOST gene showing a homozygous nonsense mutation (Trp124X) in the two patients. We reported this mutation previously in other sclerosteosis patients from a consanguineous Brazilian family. Interestingly, all three families were from the same state in Brazil, but they denied familial relationship. These patients confirm the clinical picture as found in other cases with a loss of function mutation in the SOST gene.

Density-functional study of the Mott gap in the Hubbard model

We study the Mott insulating phase of the one-dimensional Hubbard model using a local-density approximation (LDA) that is based on the Bethe Ansatz (BA). Unlike conventional functionals, the BA-LDA has an explicit derivative discontinuity. We demonstrate that as a consequence of this discontinuity the BA-LDA yields the correct Mott gap, independently of the strength of the correlations. A convenient analytical formula for the Mott gap in the thermodynamic limit is also derived. We find that in one-dimensional quantum systems the contribution of the discontinuity to the full gap is more important than that of the band-structure gap, and discuss some consequences this finding has for electronic-structure calculations.

Comparative study of van der Waals corrections to the bulk properties of graphite.

Graphite is a stack of honeycomb (graphene) layers bound together by nonlocal, long-range van der Waals (vdW) forces, which are poorly described by density functional theory (DFT) within local or semilocal exchange-correlation functionals. Several approximations have been proposed to add a vdW correction to the DFT total energies (Stefan Grimme (D2 and D3) with different damping functions (D3-BJ), Tkatchenko-Scheffler (TS) without and with self-consistent screening (TS  +  SCS) effects). Those corrections have remarkly improved the agreement between our results and experiment for the interlayer distance (from 3.9 to 0.6%) [corrected] and high-level random-phase approximation (RPA) calculations for interlayer binding energy (from 69.5 to 1.5%). [corrected]. We report a systematic investigation of various structural, energetic and electron properties with the aforementioned vdW corrections followed by comparison with experimental and theoretical RPA data. Comparison between the resulting relative errors shows that the TS  +  SCS correction provides the best results; the other corrections yield significantly larger errors for at least one of the studied properties. If considerations of computational costs or convergence problems rule out the TS  +  SCS approach, we recommend the D3-BJ correction. Comparison between the computed π(z)Γ-splitting and experimental results shows disagreements of 10% or more with all vdW corrections. Even the computationally more expensive hybrid PBE0 has proved unable to improve the agreement with the measured splitting. Our results indicate that improvements of the exchange-correlation functionals beyond the vdW corrections are necessary to accurately describe the band structure of graphite.

Density-Functional Theory for the Hubbard Model: Numerical Results for the Luttinger Liquid and the Mott Insulator

We construct and apply an exchange-correlation functional for the one-dimensional Hubbard model. This functional has built into it the Luttin-ger-liquid and Mott-insulator correlations, present in the Hubbard model, in the same way in which the usual ab initio local-density approximation (LDA) has built into it the Fermi-liquid correlations present in the electron gas. An accurate expression for the exchange-correlation energy of the homogeneous Hubbard model, based on the Bethe Ansatz (BA), is given and the resulting LDA functional is applied to a variety of inhomo-geneous Hubbard models. These include finite-size Hubbard chains and rings, various types of impurities in the Hubbard model, spin-density waves, and Mott insulators. For small systems, for which numerically exact diagonalization is feasible, we compare the results obtained from our BA-LDA with the exact ones, finding very satisfactory agreement. In the opposite limit, large and complex systems, the BA-LDA allows to investigate systems and parameter regimes that are inaccessible by traditional methods.

Magnetic susceptibility of a two-channel Anderson model

Temperature-dependent magnetic susceptibility is calculated for a two-channel Anderson model, by using the numerical renormalization group plus an interleaving procedure to recover the continuum of the conduction band. Fermi- and non-Fermi-liquid fixed points can be obtained in the low-temperature regime of the model susceptibility.

Renormalization-group calculation of dynamical properties for impurity models

Abstract The numerical renormalization-group method was originally developed to calculate the thermodynamical properties of impurity Hamiltonians. A recently proposed generalization capable of computing dynamical properties is discussed. As illustrative applications, essentially exact results for the impurity specttral densities of the spin-degenerate Anderson model and of a model for electronic tunneling between two centers in a metal are presented.

Optical and fundamental band gaps disparity in transparent conducting oxides: new findings for the In2O3 and SnO2 systems

The optical band gap, extracted from absorption measurements, defines the figure of merit for transparent conducting oxides (TCOs). In many oxides, such as [Formula: see text] or [Formula: see text], inversion symmetry introduces a selection rule that blocks transitions from the valence-band maximum to the conduction-band minimum. This raises the absorption threshold and enlarges the optical gap relative to the fundamental band gap. Here, we present density-functional computations identifying two optical gaps, either of which can be detected, depending on the optical light intensity. Under strong illumination, weak transitions from [Formula: see text]-points near the valence-band maximum contribute significantly to the absorption spectrum and define an optical gap matching the fundamental gap. Low optical intensities by contrast give prominence to the large optical gap determined by the selection rule. While experimental conditions have favored observation of the former optical gap in [Formula: see text], in contrast, absorption measurements in [Formula: see text] have focused on the latter. Our findings explain the disparity between the optical and fundamental gaps in bixbyite [Formula: see text] and predict that, measured under low illumination, the optical gap for rutile [Formula: see text] will increase, from 3.60 eV to 4.34 eV.

Determinação do tamanho do fígado de crianças normais, entre 0 e 7 anos, por ultrassonografia

OBJECTIVE: The present study was aimed at sonographically determining the liver size in healthy newborns, infants and children under 7 years of age, correlating results with age, sex, height, body weight and body mass index. MATERIALS AND METHODS: A total of 584 healthy children subdivided into 11 age groups were evaluated with measurements of the left lobe craniocaudal diameter at the midsternal line, and the craniocaudal diameter of the right lobe posterior surface at the midclavicular line. The following tests were utilized for statistical analysis: a) Pearsons correlation coefficient (correlation study); b) non-paired Students t-test (comparison of measures between sexes); c) nonlinear regression models (nomograms). RESULTS: The liver size presented a progressive growth from the birth up to the age of 7, proportionally lower than the body growth, in correlation with age, height and body weight (r > 0.70). Correlation with the body mass index was not observed (r < 0.11). There was no significant difference in liver size between male and female individuals. CONCLUSION: Liver size was sonographically determined in healthy children under the age of 7 by means of a standardized method, demonstrating a strong correlation with age and anthropometric indicators. Nomograms demonstrate the typical variations of the liver size in the population evaluated with a different growth pattern for each hepatic lobe.