Effects of van der Waals interaction for first-principles calculations on iron-based superconductors

• van der Waals density functional calculations for iron-based superconductors.
• Optimized structures are evaluated.
• van der Waals density functional reproduce lattice constants of FeSe.
• Except for FeSe, van der Waals interaction hardly affects crystal structures.

We investigate effects of van der Waals (vdW) interaction on various iron-based superconductors by first-principles calculations based on the van der Waals density functional (vdW-DF) taking account of non-local and long range interaction. vdW-DF reproduces well the lattice constants of FeSe, while the crystal structure of other iron-based superconductors are not so sensitive to vdW interaction. These results suggest that the effects of vdW interaction on layered superconductors are often essential although they depend on the characters of the interlayer couplings.