Improving the Description of Nonmagnetic and Magnetic Molecular Crystals via the van der Waals Density Functional

We have derived and implemented a stress tensor formulation for the van derWaals density functional (vdW-DF) with spin-polarization-dependent gradient correction (GC) recently proposed by the authors [J. Phys. Soc. Jpn. 82, 093701 (2013)] and applied it to nonmagnetic and magnetic molecular crystals under ambient condition. We found that the cell parameters of the molecular crystals obtained with vdW-DF show an overall improvement compared with those obtained using local density and generalized gradient approximations. In particular, the original vdW-DF with GC gives the equilibrium structural parameters of solid oxygen in the {alpha}-phase, which are in good agreement with the experiment.

Implementation of van der Waals Density Functional Approach to the Spin-Polarized System: Interaction Potential between Oxygen Molecules

We propose a practical approach to spin-polarized systems within the van der Waals density functional (vdW-DF). The method was applied to a gas phase oxygen molecule and a parallel (H-type) pair of oxygen molecules. It was found that vdW-DF improves the equilibrium distance and binding energy. In particular, one type of vdW-DF can describe such systems reasonably well. The van der Waals interaction has been confirmed to have an energy comparable to the magnetic one, while emerging at a distance rather longer than the latter.