title: Parameter-free calculations of X-ray spectra with FEFF9.
abstract: We briefly review our implementation of the real-space Green's function (RSGF) approach for calculations of X-ray spectra, focusing on recently developed parameter free models for dominant many-body effects. Although the RSGF approach has been widely used both for near edge (XANES) and extended (EXAFS) ranges, previous implementations relied on semi-phenomenological methods, e.g., the plasmon-pole model for the self-energy, the final-state rule for screened core hole effects, and the correlated Debye model for vibrational damping. Here we describe how these approximations can be replaced by efficient ab initio models including a many-pole model of the self-energy, inelastic losses and multiple-electron excitations; a linear response approach for the core hole; and a Lanczos approach for Debye-Waller effects. We also discuss the implementation of these models and software improvements within the FEFF9 code, together with a number of examples.
authors.affiliation: Department of Physics, University of Washington, Seattle, WA 98195, USA.
authors.forename: John J
authors.initials: JJ
authors.lastname: Rehr
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Kas
authors.forename: Fernando D
authors.initials: FD
authors.lastname: Vila
authors.forename: Micah P
authors.initials: MP
authors.lastname: Prange
authors.forename: Kevin
authors.initials: K
authors.lastname: Jorissen
mesh_terms: D012984:Software; D056928:X-Ray Absorption Spectroscopy