M06-2X functional was employed to study halogen-π interactions in X-C2-Y…C8H8 complexes (X, Y=H, F, Cl, and Br). In fact, interactions of mono- or di-halogenated acetylenes and planar cyclooctatetraene as an anti-aromatic π system were considered. Relationship between binding energies of the complexes and charge transfer effects was investigated. Also, electronic charge density values were calc...