Direct evaluation of the isotope effect within the framework of density functional theory for superconductors

Within recent developments of density functional theory, its numerical implementation and of the superconducting density functional theory is nowadays possible to predict the superconducting critical temperature, Tc, with sufficient accuracy to anticipate the experimental verification. In this paper we present an analytical derivation of the isotope coefficient within the superconducting density functional theory. We calculate the partial derivative of Tc with respect to atomic masses. We verified the final expression by means of numerical calculations of isotope coefficient in monatomic superconductors (Pb) as well as polyatomic superconductors (CaC6). The results confirm the validity of the analytical derivation with respect to the finite difference methods, with considerable improvement in terms of computational time and calculation accuracy. Once the critical temperature is calculated (at the reference mass(es)), various isotope exponents can be simply obtained in the same run. In addition, we provide the expression of interesting quantities like partial derivatives of the deformation potential, phonon frequencies and eigenvectors with respect to atomic masses, which can be useful for other derivations and applications

Electronic, dynamical and superconducting properties of CaBeSi

We report first-principles calculations on the normal and superconducting state of CaBe(x)Si(2-x) (x=1), in the framework of density functional theory for superconductors (SCDFT). CaBeSi is isostructural and isoelectronic to MgB2 and this makes possible a direct comparison of the electronic and vibrational properties and the electron-phonon interaction of the two materials. Despite the many similarities with MgB2 (e.g. sigma bands at the Fermi level and a larger Fermi surface nesting), according to our calculations CaBeSi has a very low critical temperature (Tc ~ 0.4 K, consistent with the experiment). CaBeSi exhibits a complex gap structure, with three gaps at Fermi level: besides the two sigma and pi gaps, present also in MgB2, the appearance of a third gap is related to the anisotropy of the Coulomb repulsion, acting in different way on the bonding and antibonding electronic pi states.Comment: 6 pages, 5 figure

Theoretical Investigation of Optical Conductivity in Ba [Fe(1-x)Co(x)]2 As2

We report on theoretical calculations of the optical conductivity of Ba [Fe(1-x)Co(x)]2 As2, as obtained from density functional theory within the full potential LAPW method. A thorough comparison with experiment shows that we are able to reproduce most of the observed experimental features, in particular a magnetic peak located at about 0.2 eV which we ascribe to antiferromagnetic ordered magnetic stripes. We also predict a large in-plane anisotropy of this feature, which agrees very well with measurements on detwinned crystals. The effect of Co doping as well as the dependence of plasma frequency on the magnetic order is also investigated

Teor de potássio no solo adubado com fontes alternativas do nutriente, sob manejo orgânico da bananeira.

As rochas naturais moídas têm sido utilizadas na agricultura, principalmente os calcários e os fosfatos naturais. As rochas contendo flogopita ou biotita podem ser avaliadas como fontes alternativas de potássio (K) para uso na agricultura. Alguns desses tipos de rochas são os kamafugitos, flogopititos, biotititos, kimberlitos, biotita xistos e outras. No sistema orgânico o K torna-se mais limitante, pois as plantas, principalmente as fruteiras são muito exigentes no nutriente. O potássio é o nutriente mais absorvido pela bananeira, sendo para ?Prata Anã? em torno de 34,79 kg de K (42,15 kg de K2O) por tonelada de frutos produzidos. Uma fonte utilizada em cultivos orgânicos é o sul-po-mag (22% de K2O), cujo preço é superior ao das fontes tradicionais. Acredita-se que a aplicação de rochas silicáticas moídas pode contribuir com quantidades significativas de K para a cultura a médio e a longo prazos, principalmente para sistemas orgânicos, onde a fonte solúvel mais utilizada (KCl) não é permitida. Objetivou-se avaliar o teor de potássio no solo cultivado com bananeira com aplicação de doses crescentes de flogopitito, comparando com o sul-po-mag.PDF. 037

Static and Dynamical Susceptibility of LaO1-xFxFeAs

The mechanism of superconductivity and magnetism and their possible interplay have recently been under debate in pnictides. A likely pairing mechanism includes an important role of spin fluctuations and can be expressed in terms of the magnetic susceptibility chi. The latter is therefore a key quantity in the determination of both the magnetic properties of the system in the normal state, and of the contribution of spin fluctuations to the pairing potential. A basic ingredient to obtain chi is the independent-electron susceptibility chi0. Using LaO1-xFxFeAs as a prototype material, in this report we present a detailed ab-initio study of chi0(q,omega), as a function of doping and of the internal atomic positions. The resulting static chi0(q,0) is consistent with both the observed M-point related magnetic stripe phase in the parent compound, and with the existence of incommensurate magnetic structures predicted by ab-initio calculations upon doping.Comment: 15 pages, 8 figure

Efeito da aplicação de boro em solo de Tabuleiro Costeiro na produção do maracujazeiro.

A cultura do maracujá está em franca expansão tanto para a produção de frutos para consumo in natura como para suco. O Brasil é o primeiro produtor mundial de maracujá, com produção aproximada de 684 mil toneladas em 48.752 hectares. O Estado da Bahia destaca-se como o maior produtor com 275 mil toneladas (40 % da produção nacional), onde o maracujazeiro é cultivado em solos de Tabuleiros Costeiros. Estes solos podem apresentar-se intemperizados, com baixos teores de matéria orgânica, escassez de água, altos teores de ferro e alumínio, levando assim, a deficiência de boro (B) nas plantas de maracujá. O boro desempenha importante papel na migração e metabolismo de carboidratos, facilitando o transporte dos açúcares através das membranas. A deficiência de B inibe ou paralisa o crescimento dos tecidos meristemáticos da parte aérea e das raízes. As plantas de maracujá deficientes em B apresentam inicialmente atrofia e posteriormente, necrose da gema terminal podendo ocorrer ou não o brotamento de gemas laterais logo abaixo da gema atrofiada. Ocorrem ainda, clorose irregular e manchas necróticas nas margens das folhas. Assim, considerando a possível limitação de boro em solos de Tabuleiros Costeiros, objetivou-se avaliar o efeito desse nutriente na produção do maracujá amarelo.PDF. 036