Can density functional theory methods be used to simulate the ε phase of solid oxygen?

We present density functional theory (DFT) calculations of the (O ₂)₄ cluster to shed light into the applicability of DFT methods to studies of the ε phase of solid oxygen. For the lower pressure range, loose clusters, DFT calculations cannot reproduce the nature of the interaction, producing artificial overbinding. For more compact geometries, single configuration character appears and some of the functionals studied agree well with benchmark calculations. In this situation -corresponding to higher pressures - a simple structural model of the solid leads to quite good agreement of the DFT predictions with measurements of the pressure dependence of the intra- and inter-clusters distances.