Spectral and Fermi surface properties from Wannier interpolation

We present an efficient first-principles approach for calculating Fermi surface averages and spectral properties of solids, and use it to compute the low-field Hall coefficient of several cubic metals and the magnetic circular dichroism of iron. The first step is to perform a conventional first-principles calculation and store the low-lying Bloch functions evaluated on a uniform grid of k-points in the Brillouin zone. We then map those states onto a set of maximally-localized Wannier functions, and evaluate the matrix elements of the Hamiltonian and the other needed operators between the Wannier orbitals, thus setting up an ``exact tight-binding model.'' In this compact representation the k-space quantities are evaluated inexpensively using a generalized Slater-Koster interpolation. Because of the strong localization of the Wannier orbitals in real space, the smoothness and accuracy of the k-space interpolation increases rapidly with the number of grid points originally used to construct the Wannier functions. This allows k-space integrals to be performed with ab-initio accuracy at low cost. In the Wannier representation, band gradients, effective masses, and other k-derivatives needed for transport and optical coefficients can be evaluated analytically, producing numerically stable results even at band crossings and near weak avoided crossings.Comment: 12 pages, 7 figure

Symmetry Aspects in Nonrelativistic Multi-Scalar Field Models and Application to a Coupled Two-Species Dilute Bose Gas

We discuss unusual aspects of symmetry that can happen due to entropic effects in the context of multi-scalar field theories at finite temperature. We present their consequences, in special, for the case of nonrelativistic models of hard core spheres. We show that for nonrelativistic models phenomena like inverse symmetry breaking and symmetry non-restoration cannot take place, but a reentrant phase at high temperatures is shown to be possible for some region of parameters. We then develop a model of interest in studies of Bose-Einstein condensation in dilute atomic gases and discuss about its phase transition patterns. In this application to a Bose-Einstein condensation model, however, no reentrant phases are found.Comment: 8 pages, 1 eps figure, IOP style. Based on a talk given by R. O. Ramos at the QFEXT05 workshop, Barcelona, Spain, September 5-9, 2005. One reference was update

Avaliação da resistência de clones de cupuaçuzeiro a vassoura-de-bruxa.

Esse trabalho foi realizado com o objetivo de avaliar a resistência de clones de cupuaçuzeiro a doença vassoura-de-bruxa, em condições de campo, considerando a perda de frutos causada pela doença

Divergência genética entre clones de cupuaçuzeiro com base em características dos frutos.

O objetivo avaliar a diversidade genética entre 23 clones de cupuaçuzeiro, discriminando os caracteres mais importantes para a divergência genética em procedimentos multivariados. O trabalho foi realizado na Embrapa Amazônia Ocidental em Manaus, AM, em um ensaio com 23 clones. Avaliou-se 9 características do fruto. Os clones foram agrupados utilizando o método de otimização de Tocher, com base nas estimativas de distância Euclidiana média padronizada, utilizando os procedimentos de análise multivariada. Houve a formação de 11 grupos, com maior concentração no primeiro grupo. Em ordem decrescente a contribuição relativa de cada característica para a diversidade genética entre os clones foram número de sementes/fruto, percentual de casca/fruto, percentual de polpa/fruto e percentual de sementes/fruto, totalizando 84,1% de contribuição para a distribuição total, sendo portanto consideradas as mais importantes