Multicenter delocalization indices vs. properties of the electron density at ring critical points: A study on polycyclic aromatic hydrocarbons

Six-center delocalization indices, 6-DI’s, computed within Mulliken and QTAIM approaches, and properties of the electron density at ring critical points, RCP’s, (electron density and its Laplacian) are studied for a series of 27 polycyclic aromatic hydrocarbons. Both approaches reflect the same trends for the local aromaticity of benzenoid rings. Moreover, there is a linear correlation between the natural logarithm of 6-DI’s and RCP properties. The RCP properties calculated at the DFT level indicate the local aromaticity decreases from outer to inner rings in polyacenes. This contradicts previous results obtained at HF level and supports the conclusions of multicenter indices.