π-Electronic Structures of the Base Pairs of DNA

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Abstract
π-electronic structures of the base pairs of DNA are determined in the framework of Frenkel-Davydov's exciton theory including double excitations. The π-electron densities in the ground and the excited states and he excitation energies and oscillator strengths are discussed in comparison with those of the component bases. The hyperchromic effect is found in the transition to the lowest excited states and the slight blue shift in A-U pair and somewhat appreciable blue shift in G-C pair are found. Further, the interaction energies between pairing bases are estimated in terms of generalized charge densities of component bases which were calculated using the best available π-electron molecular orbitals obtained in our previous work. The π-electronic stabilization energy of base pairs mainly results from the interaction between the permanent charges in the atomic sites of the bases and it is found that G-C pair is more stable than A-U pair.