Polarization Propagator for X-Ray Spectra

A polarization propagator for x-ray spectra is outlined and implemented in density functional theory. It rests on a formulation of a resonant-convergent first-order polarization propagator approach which makes it possible to directly calculate the x-ray absorption cross section at a particular frequency without explicitly addressing the excited states. The quality of the predicted x-ray spectrum relates only to the type of density functional applied without any separate treatment of dynamical relaxation effects.

Figure 1

Molecular structure of guanine-cytosine.

Figure 2

$K$-edge NEXAFS spectrum of water. The CAM-B3LYP results are obtained with 65% (circles) and 100% (squares) long-range Coulomb interaction. The LB94 results show individual components and averaged value (solid line with circles). The spectra have been shifted by 15.15 (CAM-B3LYP) and 4.0 eV (LB94). The experimental results are taken from Ref. 9.

Figure 3

Carbon $K$-edge NEXAFS spectrum (shifted by 10 eV) of guanine-cytosine and adenine-thymine as determined with the CPP method with DFT and the CAM-B3LYP functional using 100% long-range Coulomb interaction. The absorption peaks are attributed to different atoms according to the labeling in Fig. 1.

Figure 4

Nitrogen $K$-edge NEXAFS spectrum (shifted by 14 eV) of guanine-cytosine and adenine-thymine as determined with the CPP method with DFT and the CAM-B3LYP functional using 100% long-range Coulomb interaction. The atom specific absorption (see Fig. 1 for labeling) to the total absorption (resulting solid line) is indicated.

Figure 5

Oxygen $K$-edge NEXAFS spectrum (shifted by 15 eV) of guanine-cytosine and adenine-thymine as determined with the CPP method with DFT and the CAM-B3LYP functional using 100% long-range Coulomb interaction. The absorption peaks are attributed to different atoms according to the labeling in Fig. 1, and the absorption contributions for different light polarization is indicated.