An analysis of the remaining error sources in projection-based WF-in-DFT embedding showed that the main problem is the non-additive exchange-correlation energy , for which an MP2-type correction was proposed. In the context of transition-metal chemistry, this topic has been picked up in our (JN's) lab . It was shown that WF-in-DFT embedding can actually lead to worse results than DFT-in-DFT embedding for the same system, since the "improved" wavefunction description of the active system destroys the error cancellation between errors in the active-system's energy and the interaction energy.