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Hybrid functionals often improve considerably the accuracy ofdensity-functional calculations, in particular of quantities resulting from theband structure. In plane-wave (PW) calculations this benefit comes at the costof an increase in computation time by several orders of magnitude. For thisreason, large-scale problems addressed within the PW formalism have to rely onpre-relaxed atomistic geometries, obtained with cheaper local or semi-localexchange-correlation functionals. We investigate how suitable these geometriesare when plugged into single-point hybrid-DFT calculations. Based on severalcase studies, we find two important sources of error originating from (i) bondstrain and (ii) over-mixing between defect and crystalline states. The firstarises from the mismatch between the pre-relaxed geometry and that obtainedafter a subsequent hybrid-DFT-level relaxation. The second occurs when defectstates edging an underestimated band gap artificially mix with crystallinestates, affecting the local bonding character of the defect, and thereforeleading the spurious hybrid-DFT energies. Due to cancelation effects, thelingering strain contributes little ($\lesssim10$ meV) to the error bar ofquantities based on energy differences of pre-relaxed structures. The errorfrom state over-mixing does not benefit from cancelation effects and has to bemonitored with caution.

Can we rely on hybrid-DFT energies of solid-state problems with local-DFT geometries?