An ab initio study of the monomeric and dimeric forms of group 13 metal halides in model electrophilic aromatic substitution reaction has been performed. Several computational approaches have been tested. It is found that MP2/LANL2DZ(d)+ results are in good agreement with experiment, in contrast to data obtained at MP2/DZP and MP4/DZP++//MP2/DZP levels of theory. Formation of C₆H₇⁺ · M₂Cl₇ ion pairs is more favorable compared to C₆H₇^- · MCl₄^-, for both Al and Ga, which suggests that dimeric forms of the metal halides should play a significant role in the electrophilk aromatic substitution reactions.