DFT study on the intermolecular interactions between Aun (n = 2-4) and thymine

The interaction between small gold clusters and thymine was studied using density functional method (DFT). Geometries of neutral thymine with Aun (n = 2-4) clusters were optimized using the B3LYP method. The 6-31G+(d,p) basis set was used for thymine and the Stuttgart/Dresden effective core potential (ECP) basis set SDD was employed for the gold atom. Structural parameters and energy properties were discussed for the optimized complexes stabilized with the AuO anchoring bond and the nonconventional Au···HN hydrogen bond. The calculated interacting energy results show that the binding of Aun is the most strong at thymine (H1,O2) site, whereas its binding at (H3,O2) displays relatively weaker stability. Furthermore, analysis of the charge distributions of the optimized complexes by using the natural bond orbital analysis indicates charge is transferred from the lone pair of oxygen in thymine to the n* and σ* orbitals of Au during the interaction. The calculated second-order perturbation stabilization energies show that the AuO anchoring bond plays an important role in forming the Aun·Thymine complexes.