Thirty-two nucleic acid hydrogen-bonded base pairs have been examined using second-order Moller-Plesset perturbation theory (MP2) and the 6-31G~*(0.25) and modified aug-cc-pVDZ basis sets. Complexes of C-s symmetry have been constructed from rigid monomers which allowed us to use a compact parametrication of their geometry based on the centre of mass separation and Euler angles. The dependence of the interaction energy and its components on small geometrical modifications around the minima have been examined. The electrostatic and the exchange energies have been found to be the most important components of the overall interaction energy, although the dispersion and the induction energies also play important roles. The exchange energy, while typically not the largest in magnitude at the minima, is the most anisotropic component for rotations of the monomers in the plane of the complex. The analysis of the electron-correlated components reveals that the effect of the attractive dispersion energy is to a large degree canceled out by the repulsive correlation correction to the exchange energy.
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