Dielectric screening in extended systems using the self-consistent Sternheimer equation and localized basis sets

We develop a first-principles computational method for investigating the dielectric screening in extended systems using the self-consistent Sternheimer equation and localized non-orthogonal basis sets. Our approach does not require the explicit calculation of unoccupied electronic states, only uses two-center integrals, and has a theoretical scaling of order O(N^3). We demonstrate this method by comparing our calculations for silicon, germanium, diamond, and LiCl with reference planewaves calculations. We show that accuracy comparable to planewaves calculations can be achieved via a systematic optimization of the basis set.Comment: 6 pages, 3 figure

Raman scattering study of electron-doped Prx_xCa1−x_{1-x}Fe2_2As2_2 superconductors

Temperature-dependent polarized Raman spectra of electron-doped superconducting Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$ ($x \approx 0.12$) single crystals are reported. All four allowed by symmetry even-parity phonons are identified. Phonon mode of B$_{1g}$ symmetry at 222 cm$^{-1}$, which is associated with the c-axis motion of Fe ions, is found to exhibit an anomalous frequency hardening at low temperatures, that signals non-vanishing electron-phonon coupling in the superconducting state and implies that the superconducting gap magnitude $2\Delta_c < 27$meV.Comment: 4 pages, 3 figure

Isotope effects on the lattice parameter of cubic SiC

Path-integral molecular dynamics simulations in the isothermal-isobaric (NPT) ensemble have been carried out to study the dependence of the lattice parameter of 3C-SiC upon isotope mass. This computational method allows a quantitative and nonperturbative study of such anharmonic effect. Atomic nuclei were treated as quantum particles interacting via a tight-binding-type potential. At 300 K, the difference Delta a between lattice parameters of 3C-SiC crystals with 12C and 13C amounts to 2.1 x 10^{-4} A. The effect due to Si isotopes is smaller, and amounts to 3.5 x 10^{-5} A when replacing 28Si by 29Si. Results of the PIMD simulations are interpreted in terms of a quasiharmonic approximation for the lattice vibrations.Comment: 4 pages, 3 figure

Age problem in holographic dark energy

We study the age problem of the universe with the holographic DE model introduced in [21], and test the model with some known old high redshift objects (OHRO). The parameters of the model have been constrained using the SNIa, CMB and BAO data set. We found that the age of the old quasar APM 08 279+5255 at z = 3.91 can be described by the model.Comment: 13 page

Impuesto Diferido bajo NIIF: Impacto en empresas intensivas en propiedades, planta y equipos

En Colombia ha sido poco frecuente el registro en los estados financieros del impuesto diferido, a pesar de la obligatoriedad como mecanismo de asignación y reconocimiento de impuestos, establecida en los decretos 2649 y 2650 de 1993 y que incide en los resultados, asignación real de utilidades y flujos de caja futuros; sin embargo, se espera que esto cambie a partir de la adopción de las Normas Internacionales de Información Financiera. El objetivo del trabajo es determinar el impacto que tendrá en las organizaciones la aplicación de la norma internacional NIC 12 en lo referente al impuesto a las ganancias e impuesto diferido, originado en el rubro de propiedades, planta y equipo. Para lograrlo, se inicia con una identificación del modelo contable actual bajo norma colombiana, se compara con el estándar o norma internacional, y se determinan las diferencias conceptuales y de medición y se analizan dos casos reales, para calcular impactos del impuesto bajo los lineamientos de la NIC 12 y otros resultados. Uno de los principales efectos esperados y que fue validado en el presente análisis por la adopción de las NIIF, en las compañías intensivas en activos fijos, es el impacto negativo al patrimonio de los accionistas por la determinación del impuesto diferido, el cual surge de aplicar las tasas impositivas a las diferencias temporales de los activos y pasivos medidos para fines contables y tributarios.In Colombia has been infrequent of registration in the financial statements of deferred tax, despite the obligation as a mechanism for allocation and recognition of tax, established in decrees 2649 and 2650 of 1993 and affects the results, actual allocation of profits and future cash flows; however, this is expected to change from the adoption of International Financial Reporting Standards. The aim of the study is to determine the impact it will have on the organizations implementing the international standard IAS 12 Income Taxes, originated in the category of property, plant and equipment. To achieve this, it starts with an identification of the current accounting model under Colombian norm Deferred tax is compared with standard or international standard, seeking to determine the conceptual and measurement differences; two real cases are taken and the tax calculation under the guidelines of IAS 12 is performed. One of the main expected and was validated in this analysis by the adoption of IFRS in intensive companies in fixed assets, effects is the negative impact on shareholders' equity for the determination of deferred taxes, which arises from applying the tax on temporary differences of assets and liabilities measured for accounting and tax purposes rates