Effect of the Donor-Acceptor Energy Gap

To study the effect of the energy gap between donor and acceptor, we carried out HF/6-31G calculations on [(GC),(AT)] [41] and compared various procedures for determining the coupling elements within the one-electron approximation. In the complex [(GC),(AT)], guanine and adenine act as donor and acceptor sites. The donor-acceptor energy gap can be modulated by ap- 

If the strength of the electric field increases, the donor-acceptor gap grows, the charge on guanine becomes progressively smaller Aq becomes more negative), and the difference of the dipole moments increases 

In summary, these computational results suggest that the GMH and FCD methods are quite robust and can be applied to DNA fragments where donor and acceptor levels are far from resonance. On the other hand, the results demonstrate that the electron-transfer matrix element does not vary significantly when a perturbation by an external electric field is applied. This find- 

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