The molecular structure of the parallel orientation of the p-chlorobenzoic acid dimer has been studied at the second-order Møller-Plesset level using split-valence-quality basis sets augmented by polarization functions. In the obtained dimer structure, the Cl atoms are located behind the carboxyl groups of the neighboring monomer, while in crystalline copper and nickel p-chlorobenzoate complexes, the Cl atoms and the benzene nuclei form a parallel displaced umbrella structure with the Cl atoms mutually above the center of the respective benzene ring. The interaction energy for the parallel p-chlorobenzoic acid dimer complex is calculated at the second-order Møller-Plesset level to be 5.1 kcal mol -1 . The intermolecular attraction is mainly due to dispersion effects between the aromatic rings. The obtained distance between the benzene nuclei of 343 pm is in agreement with the experimental values of 341.6 and 366.6 pm measured for nickel and copper p-chlorobenzoate complexes, respectively. At the second-order Møller-Plesset level, the umbrella structure is found to be bound by 2.6 kcal mol -1 , as compared to infinite separations, with a chlorine-ring distance of 364 pm. However, at the second-order Møller-Plesset level, the umbrella structure is not a local minimum.