Atomic Additivity of the Correlation Energy in Molecules by the DFT-B3LYP Scheme

Abstract

The problem of the electron correlation in the DFT-B3LYP method is considered. It is suggested that the effective correlation energy can be retrieved by a difference = E(B3LYP) − E(HF). Subsequently, it is shown that exhibits remarkable atomic additivity, similar to that found earlier for ab initio MP2, MP3, MP4, and G3 methods. Performance of the additivity formula in reproducing the B3LYP correlation energies of Lewis' systems described by a single dominant resonance structure is astonishing as evidenced by AAD = 1.3 kcal/mol and R2 = 0.99999. The effective correlation energies span a very large range of values extending from 199 to 1963 for the cc-pVDZ basis sets and from 204 to 1980 (in kcal/mol) if the G3Large basis set is employed. The calculations can be performed on the back of an envelope by elementary arithmetic operations. Importantly, it is shown that there is a close relation between and the correlation energy calculated by the G3 computational scheme. Moreover, it turns out that their differ...