Estimating Electronic Couplings from Overlap Integrals

Estimating Electronic Couplings from Overlap Integrals 

To a first approximation, the matrix element Hda is proportional to the overlap Sda for d-a distances of interest in DNA. Therefore, the couphng Vda, as given by Eq. 5, is approximately proportional to the overlap Sda- Troisi and Orlandi found an almost hnear relationship between the electronic couphng of nucleobases and the overlap of the pertinent donor and acceptor orbitals. At the level HF/3-21G, the matrix element Vda (in oV) can be estimated as —0.716 Sjj, where Sg is the overlap integral calculated between the HOMOs of the donor and acceptor sites. This approximation obviously can be very useful when combined with MD simulations of DNA fragments. However, two remarks are in order (i) the reference values of Vda should be generated with a more accurate method, e.g., based on Eq. 5 instead of Eq. 6 [32] and (ii) the very small basis set 3-2IG is insufficient for achieving satisfactory reference matrix elements (Table 1). 

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Estimating Electronic Couplings from Overlap Integrals... 

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