Theoretical optical and x-ray spectra of liquid and solid H_2O

Theoretical optical and x-ray spectra of model structures of water and ice are calculated using a many-body perturbation theory, Bethe-Salpeter equation (BSE) approach implemented in the valence- and core-excitation codes AI2NBSE and OCEAN. These codes use ab initio density functional theory wave functions from a plane-wave, pseudopotential code, quasi-particle self energy corrections, and a BSE treatment of particle-hole interactions. The approach improves upon independent-particle methods through the inclusion of a complex, energy-dependent self energy and screened particle-hole interactions to account for inelastic losses and excitonic effects. These many-body effects are found to be crucial for quantitative calculations of ice and water spectra

Electron degeneracy and intrinsic magnetic properties of epitaxial Nb:SrTiO3_3 thin-films controlled by defects

We report thermoelectric power experiments in e-doped thin films of SrTiO$_3$ (STO) which demonstrate that the electronic band degeneracy can be lifted through defect management during growth. We show that even small amounts of cationic vacancies, combined with epitaxial stress, produce a homogeneous tetragonal distortion of the films, resulting in a Kondo-like resistance upturn at low temperature, large anisotropic magnetoresistance, and non-linear Hall effect. Ab-initio calculations confirm a different occupation of each band depending on the degree of tetragonal distortion. The phenomenology reported in this paper for tetragonally distorted e-doped STO thin films, is similarto that observed in LaAlO$_3$/STO interfaces and magnetic STO quantum wells.Comment: 5 pages, 5 figure

Ab initio analysis of the x-ray absorption spectrum of the myoglobin-carbon monoxide complex: Structure and vibrations

We present a comparison between Fe K-edge x-ray absorption spectra of carbonmonoxy-myoglobin and its simulation based on density-functional theory determination of the structure and vibrations and spectral simulation with multiple-scattering theory. An excellent comparison is obtained for the main part of the molecular structure without any structural fitting parameters. The geometry of the CO ligand is reliably determined using a synergic approach to data analysis. The methodology underlying this approach is expected to be especially useful in similar situations in which high-resolution data for structure and vibrations are available.Comment: 13 pages, 3 figure

La recerca sociolingüística educativa escolar als països de llengua catalana: elements per a un balanç

Aquest article delimita l'àrea de treball de la sociolingüística educativa, en descriu el procés de formació als territoris de llengua catalana, fa un mapa dels principals grups que treballen i suggereix alguns elements per tal de fer un balanç de les seves respectives aportacions. L'autor assenyala com a tret distintiu d'aquesta àrea la important contribució de la psicologia de la llengua i el pes que hi han tingut els plantejaments bilingüistes i liberals d'autors com Miquel Siguan. Finalment, s'argumenta que ara comara l'etiqueta lingüística educativa no respon adequadament a la recerca sobre llengua i educació, i proposa de diferenciar entre una educació lingüística, definida per la seva orientació pedagògica i educativa, i una sociolingüística educativa, d'orientació més lingüística i social.School education sociolinguistic research in Catalan-speaking territories: assessment elements. This paper defines educational sociolinguistics as a research area, describes the process leading to the formation of this area in Catalan speaking territories, identifies the main groups working on it and suggests a number of elements to assess their respective contributions. The author claims that one of the distinctive features of this area lies in the important contribution from psycholinguistics, as well as the bilingualist and liberal approaches proposed by authors like Miquel Siguan. Finally, it is argued that the area usually covered by educational linguistics is better understood if a distinction is made between linguistic education, which focuses on pedagogic and educational matters, and educational sociolinguistics, that is more oriented towards linguistic and social issues

Cumulant expansion for phonon contributions to the electron spectral function

We describe an approach for calculations of phonon contributions to the electron spectral function, including both quasiparticle properties and satellites. The method is based on a cumulant expansion for the retarded one-electron Green's function and a many-pole model for the electron self-energy. The electron-phonon couplings are calculated from the Eliashberg functions, and the phonon density of states is obtained from a Lanczos representation of the phonon Green's function. Our calculations incorporate ab initio dynamical matrices and electron-phonon couplings from the density functional theory code ABINIT. Illustrative results are presented for several elemental metals and for Einstein and Debye models with a range of coupling constants. These are compared with experiment and other theoretical models. Estimates of corrections to Migdal's theorem are obtained by comparing with leading order contributions to the self-energy, and are found to be significant only for large electron-phonon couplings at low temperatures