The additivity of the π-electron correlation energy in planar heteroatomic molecules Original Research Article

We have shown that the π-electron correlation energy of planar chain and branched polyenes containing various heteroatoms follows simple additivity rules. It is a multilinear function of a number of atoms of each element entering into a given compound. The same holds for the nondynamical E(ND)π and dynamical E(D)π components of the total correlation energy. It is found that the former is insensitive to the quality of the employed basis set. In contrast, the dynamical correlation is strongly dependent on the intricacy of utilized basis sets. These findings are rationalized by taking into account a difference in their definitions, the different nature of E(ND)π and E(D)π correlation energies, and the way of their calculation. An extension of the completely active subspace considerably changes E(ND)π and E(D)π values and to some extent introduces changes in the total π-electron correlation. However, the additivity rule persistently holds, indicating that it is a robust property. Finally, it is shown that the E(ND)π energy can serve as a good indicator of the intrinsic (anti)aromaticity of cyclic compounds.