The C-X bond of halobenzenes (X = Cl, Br) has a dual character, its electron density being depleted in its prolongation and built-up on its sides. We have recently considered three protein or nucleic acid recognition sites of halobenzenes and quantified the energy gains that either electron-attracting substituents or electron-donating ones contribute due to such a character (El Hage et al., paper in revision). Nonadditivity was found to impact the total interaction energies. We focus here on one recognition site, that of the HIV-1 integrase, in which the halobenzene ring of the drug elvitegravir is sandwiched between a guanine and a cytosine base. We perform energy-decomposition analyses of the ab initio quantum-chemistry (QC) binding energies of the parent halobenzene ring and its derivatives with this G-C base pair. In these complexes, the nonadditivity of ?E could be traced back mostly to the polarization contribution E-pol. In view of large-scale applications to the entirety of the complex formed between the integrase, the viral DNA, and the whole drug, the analyses were performed in parallel with a polarizable molecular mechanics method, SIBFA. This method could faithfully reproduce most features of the QC energies. This is due to its use of QC-derived distributed multipoles and polarizabilities, which enable us to account for both nonisotropy and nonadditivity.