First principles calculations of the electric field gradient tensors of Ba2NaOsO6, a Mott insulator with strong spin orbit coupling

We present first principles calculations of the electrostatic properties of Ba2NaOsO6 (BNOO), a 5d1 Mott insulator with strong spin orbit coupling (SOC) in its low temperature quantum phases. In light of recent NMR experiments showing that BNOO develops a local octahedral distortion that is accompanied by the emergence of an electric field gradient (EFG) and precedes the formation of long range magnetic order (Lu et al 2017 Nat. Commun. 8 14407, Liu et al 2018 Phys. Rev. B 97 224103; Liu et al 2018 Physica B 536 863), we calculated BNOO's EFG tensor for several different model distortions. The local orthorhombic distortion that we identified as most strongly agreeing with experiment corresponds to a Q2 distortion mode of the Na-O octahedra, in agreement with conclusions given in (Liu et al 2018 Phys. Rev. B 97 224103). Furthermore, we found that the EFG is insensitive to the type of underlying magnetic order. By combining NMR results with first principles modeling, we have thus forged a more complete understanding of BNOO's structural and magnetic properties, which could not be achieved based upon experiment or theory alone.