The accuracy of dispersion-corrected calculations (DFT-D2, DFT-D3 and DFT-NL) is assessed here, with large basis sets (def2-QZVP) to avoid incompleteness effects, for the most stable structure of a real-world polyphenol dimer chosen as an appropriate model. Natural polyphenols form such complexes with pi-stacking playing a key stabilizing role. Our benchmark calculations predict its existence favored by 22-24 kcal/mol with respect to the isolated monomers, mainly driven by both pi-pi and H-bonding interactions. The adequate comparison of lower-cost DFT-based methods allowed bracketing their expected accuracy. These results thus pave the way towards reliable studies of challenging aggregation processes of natural products. (C) 2013 Elsevier B. V. All rights reserved.