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Comptes Rendus Physique
Volume 10, n° 6
pages 548-559 (juillet 2009)
Doi : 10.1016/j.crhy.2008.08.004
Ab initio theory and calculations of X-ray spectra
Théorie et calculs ab initio des spectres de rayons X
 

John J. Rehr , Joshua J. Kas, Micah P. Prange, Adam P. Sorini, Yoshinari Takimoto, Fernando Vila
Department of Physics, University of Washington, Seattle, WA 98195-1560, USA 

Corresponding author.
Abstract

There has been dramatic progress in recent years both in the calculation and interpretation of various x-ray spectroscopies. However, current theoretical calculations often use a number of simplified models to account for many-body effects, in lieu of first principles calculations. In an effort to overcome these limitations we describe in this article a number of recent advances in theory and in theoretical codes which offer the prospect of parameter free calculations that include the dominant many-body effects. These advances are based on ab initio calculations of the dielectric and vibrational response of a system. Calculations of the dielectric function over a broad spectrum yield system dependent self-energies and mean-free paths, as well as intrinsic losses due to multi-electron excitations. Calculations of the dynamical matrix yield vibrational damping in terms of multiple-scattering Debye–Waller factors. Our ab initio methods for determining these many-body effects have led to new, improved, and broadly applicable x-ray and electron spectroscopy codes. To cite this article: J.J. Rehr et al., C. R. Physique 10 (2009).

The full text of this article is available in PDF format.
Résumé

Ces dernières année ont vu des progrès spectaculaires tant dans le calcul que dans l’interprétation des différentes spectroscopies de rayons X. Cependant, pour tenir compte des effets à N corps, les calculs théoriques actuels utilisent souvent un certain nombre de modèles simplifiés, plutôt que les principes fondamentaux. Pour tenter de surmonter ces limitations, nous décrivons dans cet article plusieurs avancées récentes dans le domaine de la théorie et des codes informatiques, qui ouvrent la perspective de calculs sans paramètres incluant les effets dominants à N corps. Ces avances sont basées sur des calculs ab initio de la réponse diélectrique et vibrationelle d’un système. Des calculs de la fonction diélectrique sur une large gamme d’énergie fournissent, en fonction du système, les self-énergies et les libres parcours moyens, ainsi que les pertes intrinsèques dues aux excitations à plusieurs électrons. Des calculs de la matrice dynamique donnent l’amortissement vibrationel en fonction des facteurs de Debye–Waller à diffusion multiple. Nos méthodes ab initio pour la détermination des effets à N corps ont conduit à de nouveaux codes, améliorés et largement applicables, pour la spectroscopie des rayons X et des électrons. Pour citer cet article : J.J. Rehr et al., C. R. Physique 10 (2009).

The full text of this article is available in PDF format.

PACS : 78.70.Dm, 78.20.Ls, 75.50.Cc

Keywords : XAS, EXAFS, BSE, TDDFT




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