Bond Additivity Corrections for Quantum Chemistry Methods

New bond additivity correction (BAC) methods have been developed for the G2 method, BAC-G2, as well as for a hybrid density functional theory (DFT) Møller−Plesset (MP)2 method, BAC−hybrid. These BAC methods use a new form of BAC corrections, involving atomic, molecular, and bond-wise additive terms. These terms enable one to treat positive and negative ions as well as neutrals. The BAC-G2 method reduces errors in the G2 method due to nearest-neighbor bonds. The parameters within the BAC-G2 method only depend on atom types. Thus the BAC-G2 method can be used to determine the parameters needed by BAC methods involving lower levels of theory, such as BAC−hybrid and BAC-MP4. The BAC−hybrid method is expected to scale well for large molecules. The BAC−hybrid method uses the differences between the DFT and MP2 predictions as an indication of the method's accuracy, whereas the BAC-G2 method uses its internal methods (G1 and G2MP2) to accomplish this. A statistical analysis of the error in each of the methods is presented on the basis of calculations performed for large sets (more than 120) of molecules.