Electron interactions between nucleoside pairs in canonical B-DNA: I. Transfer integrals

The valence bond/Hartree-Fock (VB/HF) formalism [F. Castet et al., J. Phys. I (France), 1996, 6, 583; Chem. Phys. 1998, 232, 37] is applied to calculate the transfer integrals between interacting fragments in canonical B-DNA strands. To get a fully consistent picture of these terms, the VB/HF fragments should be defined as the full nucleosides that incorporate the base and the pentose group. The largest transfer integrals are found for intrastrand pairs involving the thymine base. Moreover, the latter integrals are shown to be strongly dependent on the orientation of the methyl group, which is thus an important geometrical parameter to be considered. The VB/HF transfer integrals are compared to the previously published electron coupling elements, calculated at the Hartree-Fock level using a dimer-splitting procedure. The differences and similarities between the two descriptions are analyzed in detail from the master equations of the different models.