Implementation of the projector augmented-wave LDA+U method: Application to the electronic structure of NiO

The so-called local-density approximation (LDA) plus the multiorbital mean- field Hubbard model (LDA+U) has been implemented within the all-electron pr ojector augmented-wave method, and then used to compute the insulating anti ferromagnetic ground state of NiO and its optical properties. The electroni c and optical properties have been investigated as a function of the Coulom b repulsion parameter U. We find that the value obtained from constrained L DA (U=8 eV) is not the best possible choice, whereas an intermediate value (U=5 eV) reproduces the experimental magnetic moment and optical properties satisfactorily. At intermediate U, the nature of the band gap is a mixture of charge transfer and Mott-Hubbard type, and becomes almost purely of the charge-transfer type at higher values of U. This is due to the enhancement of the oxygen 2p states near the top of the valence states with increasing U value.