Ab initio study of structural and electronic properties of copper and nickel tungstate

Calculating accurate band gaps of semiconducting and insulating materials is one of the major challenges currently facing density functional theory (DFT) calculations. The atomic and electronic structure of antiferromagnetic NiWO₄ and CuWO₄ is studied in the plane wave based program VASP using pure, as well as hybrid forms of the exchange-correlation (xc) functional. It is shown that the atomic structure and the electronic density of states (DOS) of these two systems can be described as accurately with non-hybrid functionals as with more computationally expensive hybrid functionals. NiWO₄ cell dimensions with less than 0.6% mean relative error can be achieved using the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) form of the xc functional. Lattice parameters comparable to those found with hybrid functionals for CuWO₄ can be obtained with the PBE+U correction method. The PBE+U correction can also be applied to the CuWO₄ system to produce the experimental band gap. The modified Becke-Johnson (mBJ) meta-GGA gives band gaps close to experimental ranges for both the NiWO₄ and CuWO₄ systems.