Role of differential correlation energy in core ionization of pyrrole and pyridine

Δ Hartree-Fock (Δ HF) and Δ Kohn-Sham (Δ KS) orbital theories are used to calculate C(1s) and N(1s) core electron binding energies and chemical shifts of pyrrole and pyridine molecules. As a result, combination of Δ KS and B3LYP functional appears as a very promising approach for the determination of the core excitation/ionization energies. For the carbon series in pyridine, electronic correlation is essential in correctly predicting the relative shifts among carbon atoms. A strong dynamical differential correlation energy for carbon and nitrogen has been revealed and can be related to the large magnitude of electronic transfer from ligands to the core ionized site.