Low-magnetic moment and strong anisotropy in non-doped iron-based superconductors

We perform first-principles calculations with a specific LDA + U scheme for non-doped iron based superconductor LaFeAsO, which exhibits an antiferromagnetic ordering with an unexpected low-magnetic moment compared to the one predicted by standard first-principles calculations. Consequently, we find two stable electronic structures, one of which has the high magnetic moment ～2.0 μ_B equivalent with the previous calculation results, and another of which reproduces the low magnetic moment ～0.3 μ_B as obtained experimentally. The former is stable in U = 0, whereas the latter becomes stable in an intermediate U range. The latter well explains various anomalous features as observed experimentally.