We report here the results from theoretical calculations of the potential energy curves for three dimers of lithium phthalocyanine (LiPc) using nine types of functionals: the M06-2x, M06L, B97D, ωB97, ωB97X, ωB97XD, CAM-B3LYP, LC-ωPBE, and LC-BLYP. The results were discussed in comparison with those obtained for the dimers of magnesium phthalocyanine (MgPc). The dispersive and long-range interactions were considered in part by using these functionals. The mechanism whereby the dispersive and long-range interactions affect the geometric structures of the LiPc and MgPc dimers is discussed. The calculated results provide insight into the computational methods for both open- and closed-shell metal phthalocyanine (MPc) dimers: Although it is difficult for the CAM-B3LYP, LC-ωPBE, and LC-BLYP functionals only with the long-range corrections to evaluate weak dispersion interactions appropriately, the M06-families, ωB97-families, and B97D functionals can estimate a weak dispersion interaction well in both open- and closed-shell MPc dimers. However, the results should be used with caution against overestimation of the relative stabilities for the results of functionals considering despersion correction. © 2012 Wiley Periodicals, Inc.