Near-edge X-ray absorption fine structure of solid oxygen under high pressure: A density functional theory study

The near-edge X-ray absorption fine structure (NEXAFS) spectra and crystal structures of the ε-O8 phase and the metallic ζ-O2 phase have been investigated using full-potential linearized augmented plane-wave (FLAPW) and pseudopotential plane-wave methods. The change in NEXAFS spectra for the k-edge of the oxygen atom suggests a means for identifying the phase transition from ε-O8 to ζ-O2 experimentally. The abrupt change of the bond length L (O1-O1) induced by pressure is believed to be responsible for the phase transition. There is no pressure-induced softening behavior in our calculated phonon dispersion curves near the phase transition pressure.