Structural distortion and orbital ordering in the triangular-lattice antiferromagnet NaVO2 from first principles

Triangular-lattice antiferromagnets with the general formula ATO(2) (A = alkali metal, T = 3d transition metal) often adopt a slightly distorted crystal structure at low temperatures, accompanying a lifting of magnetic frustration and the appearance of long-range magnetic ordering and sometimes a particular orbital ordering. Taking NaVO2 as an example, we successfully demonstrate that the tiny structural distortion with a ratio of lattice parameters, a(m)/b(m) = 1.755, and the formation of orbital ordering observed in recent neutron-diffraction experiments can be well interpreted by first-principles calculations including 3d electron correlations with parameter U-eff = 3.6 eV. This distinct study on pure structural distortion is expected to be applied in other triangular-lattice antiferromagnetic systems.