The structure and energy of A-tetrads with N6-H6 center dot center dot center dot N3 H-bonds was studied using B3LYP and BH&H density functional theory. The planar A-tetrad with C-4h, symmetry is more stable than the nonplanar structures at C-4 and S-4 symmetry. This structure corresponds to a local energy minimum. The energies of the structures with N6-H6 center dot center dot center dot N1 and N6-H6 center dot center dot center dot N7 H-bonds studied previously are of similar magnitude. Structures of A-tetrad complexes with sodium and potassium were most stable at S-4 symmetry, and similarly, sandwich complexes consisting of two tetrads and a single cation were most stable at S-8 symmetry. Relative energies of sandwich complexes with different symmetries obtained with the B3LYP and BH&H methods were quite different. BH&H overestimates the interaction energies between hydrogen-bonded neighbor bases relative to B3LYP.