title: A Polarization Propagator for Nonlinear X-ray Spectroscopies.
abstract: A complex polarization propagator approach has been developed to third order and implemented in density functional theory (DFT), allowing for the direct calculation of nonlinear molecular properties in the X-ray wavelength regime without explicitly addressing the excited-state manifold. We demonstrate the utility of this propagator method for the modeling of coherent near-edge X-ray two-photon absorption using, as an example, DFT as the underlying electronic structure model. Results are compared with the corresponding near-edge X-ray absorption fine structure spectra, illuminating the differences in the role of symmetry, localization, and correlation between the two spectroscopies. The ramifications of this new technique for nonlinear X-ray research are briefly discussed.
authors.affiliation: Department of Physics, Chemistry and Biology, Linköping University , SE-581 83 Linköping, Sweden.
authors.forename: Tobias
authors.initials: T
authors.lastname: Fahleson
authors.affiliation: Division of Theoretical Chemistry and Biology, School of Biotechnology, KTH Royal Institute of Technology , SE-106 91, Stockholm, Sweden.
authors.forename: Hans
authors.initials: H
authors.lastname: Ågren
authors.affiliation: Department of Physics, Chemistry and Biology, Linköping University , SE-581 83 Linköping, Sweden.|Division of Theoretical Chemistry and Biology, School of Biotechnology, KTH Royal Institute of Technology , SE-106 91, Stockholm, Sweden.
authors.forename: Patrick
authors.initials: P
authors.lastname: Norman
mesh_terms: D011789:Quantum Theory; D056928:X-Ray Absorption Spectroscopy