Meta GGA (SCAN) + van der Waals functionals (rvv10) calculation for K-edge X-ray Raman Spectrum of the epsilon and zeta phase of solid oxygen*

Previous theoretical studies could not predict precisely the epsilon-zeta transitional pressure which was measured at 96 GPa by experiments (Weck et al., PRL 2009, 102, 255503). The GW calculation showed the transitional pressure at 50 GPa (Kim et al., RPRB 2008, 77, 092104) while the B3LYP hybrid functional could estimate the co-existence range of epsilon-zeta from 75 GPa to 145 GPa (Ochoa-Calle et al., PRB 2015 92, 085148). The combination of meta GGA(SCAN) and van der Waals functional (rvv10) was demonstrated to enhance the direct epsilon-zeta transition at 70 GPa while the lattice parameters were very closed to the experimental data (in manuscript). On the other hand, the Inelastic X-ray Scattering (IXS) was successfully used to study epsilon phase of solid oxygen (Meng et al., PNAS 2008, 105, 33). In this talk, we will discuss the evolution of calculated IXS K-edge spectra from epsilon phase to zeta phase using SCAN+rvv10. The calculated spectra will be compared to the experimental data.