Table 2.

Interaction energy components computed at the MP2/6-31G*(0.25) for the 10 considered stacked nucleic base dimers (kcal/mol)

		Optimized geometries							Experimental structures
		ΔEMP2	ΔEHF	ΔECorr	ΔEElec	R	r	Twist	ΔEMP2	ΔEHF	ΔECorr	ΔEElec	r	Twist	Φ
A	A	−8.82	4.00	−12.82	−3.21	3.3	3.31	−110	−5.91	4.19	−10.09	−1.47	3.47	30	5.26
A	C	−9.50	0.85	−10.36	−3.38	3.3	3.39	−100	−3.12	4.67	−7.79	1.43	3.62	25	5.56
A	G	−11.17	1.30	−12.48	−4.68	3.3	3.36	−240	−7.42	3.25	−10.67	−0.86	3.49	32	5.93
A	U	−9.09	1.25	−10.34	−2.79	3.3	3.48	140	−4.97	2.88	−7.86	−1.20	3.59	34	8.88
C	C	−8.26	−2.09	−6.17	−5.47	3.4	3.40	180	−1.96	3.20	−5.16	0.88	4.31	31	2.26
C	G	−9.32	−1.44	−7.88	−4.91	3.4	3.48	0	−8.75	−0.73	−8.02	−4.12	3.59	39	5.17
C	U	−8.52	−1.51	−7.02	−5.17	3.3	3.40	240	−3.80	2.20	−6.00	−0.71	4.25	31	11.74
G	G	−11.32	−0.84	−10.48	−4.25	3.4	3.42	−110	−3.39	8.47	−11.86	1.75	3.40	39	3.03
G	U	−10.63	−1.17	−9.46	−6.46	3.3	3.35	−270	−5.67	4.87	−10.54	−0.38	3.40	42	3.43
U	U	−6.53	0.46	−6.98	−4.46	3.3	3.54	180	−1.72	3.39	−5.11	1.22	4.36	33	11.78

Abbreviations: R, is the inter-planar distance between the bases for optimized structures only (Å); r is the distance between the center of the closest rings of each considered base pair (Å); Φ is the dihedral angle between the planes of the bases (degree); and the twist angle (degree).