Quantum Chemical Treatment of Electronic Couplings in DNA Fragments

Quantum Chemical Treatment of Electronic Couplings in DNA Fragments 

In our review, we distinguished two types of DNA-related donor-acceptor systems models where donor and acceptor interact directly, and models where they are separated by intervening base pairs. 

If one attempts an accurate description of the coupling between neighboring pairs, one needs to answer several general questions. How accurate is the one-electron approximation How essential are the effects of electron corre- 

In addition, several important questions arise when one discusses large DNA fragments consisting of several base pairs. Even cases where the whole system of interest can be treated by a sufficiently accurate quantum chemical method (often this is impossible), estimates of the electronic coupling within the two-state model may lead to inaccurate results, as demonstrated for tri-mer duplexes [41]. 

Obviously, the situation will be more difficult when additional approximations have to be employed, e.g., the divide-and-conquer scheme, an effective Hamiltonian or a perturbation approach. A central open question is which electronic states of the fragments have to be included so that reliable results, as compared with supermolecular calculations, can be provided. In any case, accounting for just one state per base pair will yield only semi-quantitative results. A careful analysis of this point is highly desirable for DNA-related systems. 

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