We present an all-electron implementation of the GW approximation and apply it to wurtzite ZnO. Eigenfunctions computed in the local-density approximation (LDA) by the full-potential linearized augmented-plane-wave or the linearized muffin-tin-orbital method supply the input for generating the Green function G and the screened Coulomb interaction W. A mixed basis is used for the expansion of W, consisting of plane waves in the interstitial region and augmented-wave-function products in the augmentation-sphere regions. The frequency dependence of the dielectric function is computed within the random-phase approximation (RPA), without a plasmon-pole approximation. The Zn $3d$ orbitals are treated as valence states within the LDA; both core and valence states are included in the self-energy calculation. The calculated band gap is smaller than experiment by ~1eV, in contrast to previously reported GW results. Self-energy corrections are orbital dependent and push down the deep O $2s$ and Zn $3d$ levels by ~1eV relative to the LDA. The d level shifts closer to experiment but the size of shift is underestimated, suggesting that the RPA overscreens localized states.
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Usuda et al. (2002) studied this question.