Ab initio calculations with the dynamical vertex approximation

We propose an approach for the ab initio calculation of materials with strong electronic correlations which is based on all local (fully irreducible) vertex corrections beyond the bare Coulomb interaction. It includes the so-called GW and dynamical mean field theory and important non-local correlations beyond, with a computational effort estimated to be still manageable.Comment: 8 pages, 6 figure

Weighted Density Approximation Description of Insulating YH3_3 and LaH3_3

Density functional calculations within the weighted density approximation (WDA) are presented for YH$_3$ and LaH$_3$. We investigate some commonly used pair-distribution functions G. These calculations show that within a consistent density functional framework a substantial insulating gap can be obtained while at the same time retaining structural properties in accord with experimental data. Our WDA band structures agree with those of $GW$ approximation very well, but the calculated band gaps are still 1.0-2.0 eV smaller than experimental findings.Comment: 6 Pages, 3 figure

Core excitation effects in the breakup of halo nuclei

The role of core excitation in the structure and dynamics of two-body halo nuclei is investigated. We present calculations for the resonant breakup of 11Be on protons at an incident energy of 63.7 MeV/nucleon, where core excitation effects were shown to be important. To describe the reaction, we use a recently developed extension of the DWBA formalism which incorporates these core excitation effects within the no-recoil approximation. The validity of the no-recoil approximation is also examined by comparing with DWBA calculations which take into account core recoil. In addition, calculations with two different continuum representations are presented and compared.Ministerio de Ciencia e Innovación FIS2011-28738-c02-01, FPA2009- 07653, FPA2009-08848, CSD2007-00042Junta de Andalucía FQM160, P07-FQM-0289

On the use of the VN−MV^{N-M} approximation in atomic calculations

We demonstrate that $V^{N-M}$ approximation is a good starting point for the configuration interaction calculations for many-electron atoms and ions. $N$ is the total number of electrons in the neutral atom, $M$ is the number of valence electrons. $V^{N-M}$ is the self-consistent Hartree Fock potential for a closed-shell ion with all valence electrons removed. Using of the $V^{N-M}$ approximation considerably simplifies the many-body perturbation theory for the core-valence correlations. It makes it easier to include higher-order correlations which often significantly improves the accuracy of the calculations. Calculations for krypton and barium and their positive ions are presented for illustration.Comment: 5 pages,1 figure, submitted to Phys. Rev.

Weakly Interacting Bose-Einstein Condensates Under Rotation: Mean-field versus Exact Solutions

We consider a weakly-interacting, harmonically-trapped Bose-Einstein condensed gas under rotation and investigate the connection between the energies obtained from mean-field calculations and from exact diagonalizations in a subspace of degenerate states. From the latter we derive an approximation scheme valid in the thermodynamic limit of many particles. Mean-field results are shown to emerge as the correct leading-order approximation to exact calculations in the same subspace.Comment: 4 pages, RevTex, submitted to PR

Acoustic impedance and interface phonon scattering in Bi2_2Te3_3 and other semiconducting materials

We present first principles calculations of the phonon dispersions of Bi2Te3 and discuss these in relation to the acoustic phonon interface scattering in ceramics. The phonon dispersions show agreement with what is known from neutron scattering for the optic modes. We find a difference between the generalized gradient approximation and local density results for the acoustic branches. This is a consequence of an artificial compression of the van der Waals bonded gaps in the Bi2Te3 structure when using the generalized gradient approximation. As a result local density approximation calculations provide a better description of the phonon dispersions in Bi$_{2}$Te$_{3}$. A key characteristic of the acoustic dispersions is the existence of a strong anisotropy in the velocities. We develop a model for interface scattering in ceramics with acoustic wave anisotropy and apply this to Bi2Te3 and compare with PbTe and diamond