Four-channel model: An assessment of charge transfer via the backbone in B-DNA

We model charge transfer in B-DNA, the most common form of deoxyribonucleic acid, with the aim of assessing the role of the backbone. We achieve this by employing a four-channel tight binding model, where B-DNA is analyzed at the base and backbone sites level. The significant difference of our model, with other similar models that have appeared in the literature so far, is that we have calculated all tight binding on-site energies and interaction integrals using DFT; these are not roughly estimated or guessed. We study two kinds of sequences: homopolymers and randomly generated sequences. This enables us to effectively compare the relative ease of charge transfer through the backbone channels with that of the π pathway formed by the nucleobases' frontier molecular orbitals, since the latter is highly sensitive to sequence periodicity, as it determines the degree of energy uniformity across the base-pair sequence. Results are presented for the electronic structure, the localization of the energy eigenstates, and the ease of carrier transfer. Emphasis is given to results for holes, due to the inherent unreliability of DFT calculations for excited states. We demonstrate that the backbone could be essential for B-DNA charge transfer, provided limited backbone energy disorder.