Effects of hydration and stacking interactions on the electronic structure of DNA models

The energy band structures of a cytosine, adenine, and guanine stack in the presence of water have been calculated by the ab initio crystal-orbital method. The surrounding water molecules have been simulated by arrays of point charges, using for their positions the results of previous Monte-Carlo calculations of the corresponding polynucleotides. Furthermore, the effects of internucleotide interactions have been studied on the basis of calculations on base dimer stacks in comparison to the corresponding dimers and monomers.