  Using a hybrid density-functional theory (DFT) calculation including
spin-orbit coupling (SOC), we predict that the zigzag antiferromagnetic (AFM)
ground state of the honeycomb layered compound Na2IrO3 opens the observed
insulating gap through a long-range magnetic order. We show that the effect of
SOC and the correction of self-interaction error inherent in previous local or
semilocal DFT calculations play crucial roles in predicting the band gap
formation in Na2IrO3. It is revealed that the itinerant AFM order with a strong
suppression of the Ir magnetic moment is attributed to a considerable
hybridization of the Ir 5d orbitals with the O 2p orbitals. Thus, our results
suggest that the insulating phase of Na2IrO3 can be represented as a Slater
insulator driven by itinerant magnetism.
