a E (2)(1) andE (2)(2) represent the second-order perturbation energy due to the Lp(N) →p*(P) and Lp(N) →σ*(P-O) interaction, respectively. E (2) is in kcal∙mol-1, and all other values are in a.u.
b q (PO2F) refers to the net natural population analysis (NPA) charge on the PO2F moiety, in unit of e.