First-principles description of van der Waals-bonded spin-polarized systems using vdW-DF$+U$ method---application to solid oxygen at low pressure

摘要

The description of the molecular solid phase of O$_2$, especially itsground-state antiferromagnetic insulating phase, is known to be quiteunsatisfactory within the conventional local and semilocal density functionalapproximations used in the Kohn-Sham formalism of density functional theory.The recently-developed van der Waals functionals that take into accountnonlocal correlations have also shown subpar performance in this regard. Thedifficulty lies in the subtle balance between the van der Waals interactionsand the exchange coupling between the antiferromagnetic and ferromagneticmolecule pairs in the molecular crystal. Here, we report that the DFT$+U$approach used in combination with the vdW-DF functional performs surprisinglywell in this regard, and discuss the reasoning behind this behavior. We alsoapply this approach to study the recently-reported magnetic field-induced$\theta$ phase of solid O$_2$.