Indication of water droplet formation in hydrated clusters of cytosine and adenine: An electronic structure study using B3LYP, LMP2 and PM6

The cytosine-(H2O)14 and adenine-(H2O)16 complexes were studied using B3LYP/6-31+G(d), LMP2/aug-cc-pVnZ (n = D, T) and the new semiempirical method PM6. For each complex, two optimized structures were examined: one with water molecules distributed around the central base and one with a clustering of water molecules. The clustered structures were found to be energetically favored at all levels of theory employed (except at the B3LYP level with inclusion of zero-point energy correction, where the two cytosine-(H2O)14 structures are nearly iso-energetic).