Influence of the core-valence interaction and of the pseudopotential approximation on the electron self-energy in semiconductors

State-of-the-art theory addresses single-electron excitations in condensed matter by linking density-functional theory (DFT) with many-body perturbation theory. In actual calculations it is common to employ the pseudopotential (PP) approach, where pseudo-wave-functions enter the calculation of the selfenergy, and the core-valence interaction is treated at the DFT level. In this Letter we present accurate all-electron calculations of the self-energy and systematically compare the results to those of PP calculations. The analysis for a range of different materials reveals that both above mentioned approximations are indeed problematic

Influence of laser-excited electron distributions on the x-ray magnetic circular dichroism spectra: Implications for femtosecond demagnetization in Ni

In pump-probe experiments an intensive laser pulse creates non-equilibrium excited electron distributions in the first few hundred femtoseconds after the pulse. The influence of non-equilibrium electron distributions caused by a pump laser on the apparent X-ray magnetic circular dichroism (XMCD) signal of Ni is investigated theoretically here for the first time, considering electron distributions immediately after the pulse as well as thermalized ones, that are not in equilibrium with the lattice or spin systems. The XMCD signal is shown not to be simply proportional to the spin momentum in these situations. The computed spectra are compared to recent pump-probe XMCD experiments on Ni. We find that the majority of experimentally observed features considered to be a proof of ultrafast spin momentum transfer to the lattice can alternatively be attributed to non-equilibrium electron distributions. Furthermore, we find the XMCD sum rules for the atomic spin and orbital magnetic moment to remain valid, even for the laser induced non-equilibrium electron distributions.Comment: 6 pages, 3 figure

Resolution-of-identity approach to Hartree-Fock, hybrid density functionals, RPA, MP2, and \textit{GW} with numeric atom-centered orbital basis functions

Efficient implementations of electronic structure methods are essential for first-principles modeling of molecules and solids. We here present a particularly efficient common framework for methods beyond semilocal density-functional theory, including Hartree-Fock (HF), hybrid density functionals, random-phase approximation (RPA), second-order M{\o}ller-Plesset perturbation theory (MP2), and the $GW$ method. This computational framework allows us to use compact and accurate numeric atom-centered orbitals (popular in many implementations of semilocal density-functional theory) as basis functions. The essence of our framework is to employ the "resolution of identity (RI)" technique to facilitate the treatment of both the two-electron Coulomb repulsion integrals (required in all these approaches) as well as the linear density-response function (required for RPA and $GW$). This is possible because these quantities can be expressed in terms of products of single-particle basis functions, which can in turn be expanded in a set of auxiliary basis functions (ABFs). The construction of ABFs lies at the heart of the RI technique, and here we propose a simple prescription for constructing the ABFs which can be applied regardless of whether the underlying radial functions have a specific analytical shape (e.g., Gaussian) or are numerically tabulated. We demonstrate the accuracy of our RI implementation for Gaussian and NAO basis functions, as well as the convergence behavior of our NAO basis sets for the above-mentioned methods. Benchmark results are presented for the ionization energies of 50 selected atoms and molecules from the G2 ion test set as obtained with $GW$ and MP2 self-energy methods, and the G2-I atomization energies as well as the S22 molecular interaction energies as obtained with the RPA method.Comment: 58 pages, 15 figures, and 7 table

Caracterización mecánica de la microestructura del esmalte tratado con una bebida sin alcohol

La dentición permanente, el tejido adamantino presenta una organización definida de los prismas según la zona considerada. En los 2/3 más internos del espesor, los prismas exhiben entrecruzamientos, dando origen a las bandas de Hunter- Schreger, mientras que en el tercio externo de su espesor, los prismas se disponen paralelos unos a otros, conformando el esmalte radial. Además, cada zona presenta un comportamiento biomecánico definido.Facultad de Odontologí

Efecto del agua saborizada sobre la morfología y la composición química de la microestructura del esmalte dental humano in vitro

El contenido mineral del esmalte está representado por el fosfato decacálcico hidroxiapatita. Se ha demostrado que la dureza adamantina decrece desde la superficie libre a la conexión amelodentinaria en el esmalte sano. Además, algunos elementos varían en su concentración (g%) desde la superficie externa hacia el límite amelodentinario.Facultad de Odontologí

Caracterización mecánica de la microestructura del esmalte tratado con una bebida sin alcohol

La dentición permanente, el tejido adamantino presenta una organización definida de los prismas según la zona considerada. En los 2/3 más internos del espesor, los prismas exhiben entrecruzamientos, dando origen a las bandas de Hunter- Schreger, mientras que en el tercio externo de su espesor, los prismas se disponen paralelos unos a otros, conformando el esmalte radial. Además, cada zona presenta un comportamiento biomecánico definido.Facultad de Odontologí

Study of Adsorption and Flocculation Properties of Natural Clays to Remove Prorocentrum lima

High accumulations of phytoplankton species that produce toxins are referred to as harmful algal blooms (HABs). HABs represent one of the most important sources of contamination in marine environments, as well as a serious threat to public health, fisheries, aquaculture-based industries, and tourism. Therefore, methods effectively controlling HABs with minimal impact on marine ecology are required. Marine dinoflagellates of the genera Dinophysis and Prorocentrum are representative producers of okadaic acid (OA) and dinophysistoxins responsible for the diarrhetic shellfish poisoning (DSP) which is a human intoxication caused by the consumption of shellfish that bioaccumulate those toxins. In this work we explore the use of natural clay for removing Prorocentrum lima. We evaluate the adsorption properties of clays in seawater containing the dinoflagellates. The experimental results confirmed the cell removal through the flocculation of algal and mineral particles leading to the formation of aggregates, which rapidly settle and further entrain cells during their descent. Moreover, the microscopy images of the samples enable one to observe the clays in aggregates of two or more cells where the mineral particles were bound to the outer membranes of the dinoflagellates. Therefore, this preliminary data offers promising results to use these clays for the mitigation of HABs

Benchmarking the starting points of the GW approximation for molecules

International audienceThe GW approximation is nowadays being used to obtain accurate quasiparticle energies of atoms and molecules. In practice, the GW approximation is generally evaluated perturbatively, based on a prior self-consistent calculation within a simpler approximation. The final result thus depends on the choice of the self-consistent mean-field chosen as a starting point. Using a recently developed GW code based on Gaussian basis functions, we benchmark a wide range of starting points for perturbative GW, including Hartree–Fock, LDA, PBE, PBE0, B3LYP, HSE06, BH&HLYP, CAM-B3LYP, and tuned CAM-B3LYP. In the evaluation of the ionization energy, the hybrid functionals are clearly superior results starting points when compared to Hartree–Fock, to LDA, or to the semilocal approximations. Furthermore, among the hybrid functionals, the ones with the highest proportion of exact-exchange usually perform best. Finally, the reliability of the frozen-core approximation, that allows for a considerable speed-up of the calculations, is demonstrated