Low-Energy Linear Structures in Dense Oxygen: Implications for the $\epsilon$ Phase

Using density functional theory implemented within the generalized gradient approximation, a new nonmagnetic insulating ground state of solid oxygen is proposed and found to be energetically favored at pressures corresponding to the $\epsilon$ phase. The newly predicted static ground state is composed of linear herringbone-type chains of $O_2$ molecules and has Cmcm symmetry (with an alternative monoclinic cell). Importantly, this phase supports IR-active zone-center phonons, and their computed frequencies are found to be in broad agreement with recent infrared absorption experiments.