Dicarboxylic acids are ubiquitous products of the photooxidation of volatile organic compounds which are believed to play a significant role in the formation of secondary organic aerosols in the atmosphere. In this paper, we report high-level quantum investigations of the clustering properties of sulfuric acid and benzenedicarboxylic acid molecules. Up to four molecules have been considered in the calculations, and the behavior of the three isomers of the organic diacid species have been compared. The most stable geometries have been characterized together with the corresponding thermodynamic data. From an atmospheric point of view, the results of the DFT calculations show that the organic diacid molecules may significantly enhance the nucleation of small atmospheric clusters, at least from an energetic point of view. In this respect, the phthalic acid isomer seems more efficient than the two other isomers of the benzenedicarboxylic acid, in particular because the internal distance between the two carboxyl groups in the organic diacids appears to play an important role in the stabilization of the H-bond network inside the corresponding heterocluster formed with sulfuric acid molecules.