A DFT prediction of an epsilon-zeta phase transition of solid oxygen: The SCAN+rVV10 calculation*

In the previous studies [1, 2], we carried out a DFT calculation for solid oxygen using meta-GGA+van-der-Waals functionals (SCAN+rVV10). This method enables us to reproduce the experimental interatomic distances between the two O₂ molecules in the (O₂)₄ structure of the epsilon phase at 10~20 GPa which implies that the magnetic epsilon phase is stable in that pressure range [1]. Moreover, the epsilon-zeta phase transition was studied using SCAN+rVV10 and consistently compared with our XRS measurement [2]. In this study, we discuss possibilities of a pre-phase of the zeta superconducting phase suggested by SCAN+rVV10 calculation which was not obtained by using neither PBE [3] nor hybrid-functionals [4]. The vibrational spectra and superconducting properties will be analyzed to clarify this phase from the epsilon and zeta phases.