Proton transfers within the formic acid dimer are studied using various methods. Minimum atomic basis sets yield single- and double-well potentials for single and double proton transfers, respectively, in agreement with extended basis set calculations. A potential energy surface for the decoupled proton transfers using the 4-31G basis set indicates that a simultaneous and synchronous motion of two protons is an adequate first approximation to the optimal mode of double transfer. All-electron PRDDO calculations are carried out for proton transfers within the base pairs guanine-cytosine and adenine-thymine. Single transfers are again found to be characterized by single-well potentials and double transfers by double-well potentials. Quantum mechanical tunneling rates and equilibrium constants are calculated for the most facile mode which involves a double proton transfer in the guanine-cytosine pair. The values obtained are compared to experimental data and inferences are drawn concerning the importance of the tunneling phenomenon in mutagenesis.
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Scheiner et al. (1979) studied this question.