The ratio of proton transfer reaction pathways observed in a GC base pair under the influence of an electric field applied along the three principal axes of the hydrogen bonds at 1.00 × 10⁹ V m⁻¹. The orientations for each OEEF direction are shown in Fig. 2. The ratio of reaction pathways is based on the CI-NEB reaction coordinates for 25 QM/MM replicas per electric field direction.

Electric field direction	Single proton transfer	Double proton transfer
		Total	Stepwise	Concerted
E −x	0	25	8	17
E 0 a	1	24	21	3
E +x	14	11	10	1

^aElectric fields in the positive and negative y- and z-directions (E_+y, E_−y, E_+z, and E_−z) as well as the weaker electric fields (1.00 × 10⁴ V m⁻¹ and 1.00 × 10⁷ V m⁻¹) exhibit the same ratio of proton transfer reactions as in the E₀ case.