Ab initio quantum chemical calculations of excitation energies and transition moments for the nucleic acid base monomers

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Abstract
Modern ab initio quantum chemical methods have been employed to compute excitation energies and transition moments of the nucleic acid base monomers cytosine, uradil, thymine, adenine, and guanine for the lower ir electron excited states. Full configuration interaction is allowed among the (pi)-electrons and the orbitals are optimized individually for each excited state. The multi-configurational self-consistent field method used allows full relaxation of both the (sigma)- and the (pi)-orbitals and includes correlation between the it-electrons. Basis sets of double-zeta quality have been used in these preliminary investigations. The calculated values for oscillator strengths and transition moment directions are in good agreement with experiment, where such comparisons can be made. The calculated excitation energies are, however, often too large due to the lack of (sigma)-(pi) correlation terms in the wave function.

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