  We study oxygen K-edge x-ray absorption spectroscopy (XAS) and investigate
the validity of the Zhang-Rice singlet (ZRS) picture in overdoped cuprate
superconductors. Using large-scale exact diagonalization of the three-orbital
Hubbard model, we observe the effect of strong correlations manifesting in a
dynamical spectral weight transfer from the upper Hubbard band to the ZRS band.
The quantitative agreement between theory and experiment highlights an
additional spectral weight reshuffling due to core-hole interaction. Our
results confirm the important correlated nature of the cuprates and elucidate
the changing orbital character of the low-energy quasi-particles, but also
demonstrate the continued relevance of the ZRS even in the overdoped region.
