Electronic structure of copper phthalocyanine from G₀W ₀ calculations

We present all-electron G₀W₀ calculations for the electronic structure of the organic semiconductor copper phthalocyanine, based on semilocal and hybrid density-functional theory (DFT) starting points. We show that G₀W₀ calculations improve the quantitative agreement with high resolution photoemission and inverse photoemission experiments. However, the extent of the improvement provided by G₀W₀ depends significantly on the choice of the underlying DFT functional, with the hybrid functional serving as a much better starting point than the semilocal one. In particular, strong starting-point dependence is observed in the energy positions of highly localized molecular orbitals. This is attributed to self-interaction errors (SIE), due to which the orbitals obtained from semilocal DFT do not approximate the quasi-particle (QP) orbitals as well as those obtained from hybrid DFT. Our findings establish the viability of the G ₀W₀ approach for describing the electronic structure of metal-organic systems, given a judiciously chosen DFT-based starting point.