Energy Band Structure of Models of Periodic Deoxyribonucleic Acid (DNA)

Abstract

This work originated from studies of the damage caused to DNA by radiation, damage which has been considered as one of the causes of induced cancer. It was suggested, mainly by Ladik and co-workers, that in order to understand the nature of this damage, it was first necessary to have a picture of the electronic structure of DNA, one of the problems being the degree of localization of the electrons on chains. Several attempts were made by this group to calculate the electronic structure, by considering more and more complicated periodic chains approximating more and more the true struct-ure of DNA. These calculation are critically re-viewed in the present Dissertation. The early work had been carried out on the simple Huckel model; later the Pariser-Parr-Pople approach was employed, yielding considerably different results. The inadequacies of the one-dimensional model and of other approximations are pointed out.

These calculations yielded an energy gap of over 3 eV, rather higher than experimental value. They gave fairly narrow bands, indicating that electrons cannot be de-localized over the whole chain.

One result was that the bands were narrower in in-finite chains made up of pairs of bases than in cha ins of the same nucleotide. Clearly this must be due to a smaller overlap of similar atomic orbitals because of the interposal of a different structure, and this explanation is checked in the present Dissertation by an exact calculation of the energy bands of chains of square potential wells.