A procedure is advanced for correcting the electrostatic portion of the interaction energy for the effects of intramolecular electron correlation. This expression, which specifically treats the dipole-dipole term, involves the interaction between the Hartree-Fock dipole moment of one subunit and the second-order perturbation correction of its partner (plus the converse). The algorithm is tested on 28 different DNA base pairs, whose interaction energies have been evaluated previously as a sum of the (superposition-corrected) SCF interaction plus the (London) dispersion energy. While the correlation correction is negligible for certain pairs, it is quite sizable in others, in one case lowering the long-range dipole-dipole interaction energy by 27%. On the other hand, the poor convergence of the multipole expansion at equilibrium separation leads to unsatisfactory results at this geometry. It is suggested that a distributed multipole approach would yield superior results over a wide range of intermolecular distance.
- DNA bases