We extend an approximate density functional theory ͑DFT͒ method for the description of long-range dispersive interactions which are normally neglected by construction, irrespective of the correlation function applied. An empirical formula, consisting of an R Ϫ6 term is introduced, which is appropriately damped for short distances; the corresponding C 6 coefficient, which is calculated from experimental atomic polarizabilities, can be consistently added to the total energy expression of the

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... d. We apply this approximate DFT plus dispersion energy method to describe the hydrogen bonding and stacking interactions of nucleic acid base pairs. Comparison to MP2/6-31G*͑0.25͒ results shows that the method is capable of reproducing hydrogen bonding as well as the vertical and twist dependence of the interaction energy very accurately.