Magnetism and vibrations in the phase ϵ of oxygen

Abstract Sandwiched between a set of magnetic phases at lower pressure, and a non magnetic phase at higher pressure, the magnetic state of phase ϵ of oxygen has so far been elusive, together with its crystal structure. Neutron diffraction data indicate an absence of antiferromagnetism, but do not exclude a ferromagnetic order. The recent refinement of the internal atomic positions from single-crystal diffraction finally provides us with a correct structural model to study the possible occurrence of a magnetic ground state. By employing non-collinear spin-polarized density-functional theory we show that the ground state of ϵ -O 2 is non magnetic. We also calculate vibrational spectra and show that ϵ -O 2 possesses an additional vibron mode with large Raman cross section, not seen in experiments yet.