  We report on our calculations of the inner-sphere reorganization energy and
the interaction of the pi orbitals within DNA oligomers. The exponential
decrease of the electronic coupling between the highest and second highest
occupied base orbitals of the intrastrand nucleobases in the (A-T)n and (G-C)n
oligomers have been found with an increase of the sequence number n in the DNA
structure. We conclude that for realistic estimation of the electronic coupling
values between the nucleobases within the DNA molecule, a DNA chain containing
at least four base pairs is required. We estimate the geometry relaxation of
the base pairs within the (A-T)n and (G-C)n oligomers (n=1-6) due to their
oxidation. The decrease of the inner-sphere reorganization energy with
elongation of the oligomer structure participating in the oxidation process
have been observed. The maximum degree of geometry relaxation of the nucleobase
structures and correspondingly the higher charge density in the oxidized state
are found to be located close to the oligomer center.
