Abstract
is unusual for an intermetallic compound in displaying a semiconducting gap, on the order of 0.5 eV. Conventional density-functional based electronic-structure calculations in the local-density approximation (LDA) give a similar gap but it is expected that Fe, a transition metal, is likely to display an on-site Coulomb repulsion that should be taken into account, particularly in an insulating compound with some narrow bands. We analyze first-principles LDA calculations for , and then include on-site Coulomb repulsion in a mean-field way ( method) to show that, with the moderate value on the order of 2 eV, one obtains Fe moments in antialigned dimers (band theory “singlets”) with a band gap that still coincides with the observed gap. Counterintuitively, increasing the value of gradually reduces the gap and finally produces an incorrect metallic state. We suggest that more experimental study should be done to distinguish between the “ singlet” and nonmagnetic descriptions and provide calculations of the optical properties for comparison with data.
- Received 16 August 2010
DOI:https://doi.org/10.1103/PhysRevB.82.155202
©2010 American Physical Society