In order to compute the proton affinity of a phenolic analogue such as hydroxytyrosol the following equation is used:

PA = HArO-  + HH+ - HArOH

where H is enthalpy of species. I used Gaussian 09 to calculate the above enthalpies. For the neutral molecule, the enthalpy HArOH was calculated with the method wB97X/aug-cc-pVTZ. The question is if the enthalpy HArO- of the hydroxytyrosol anion should be computed rwB97X/aug-cc-pVTZ or uB97X/aug-cc-pVTZ?