Description of adenine and cytosine on Au(111) nano surface using different DFT functionals (PW91PW91, wB97XD, M06-2X, M06-L and CAM-B3LYP) in the framework of ONIOM scheme: Non-periodic calculations

In this work, the adsorption of the adenine (AD) and cytosine (CY) on the Au(111) nano surface ([email protected] and [email protected]) have been examined in the framework of combined quantum mechanics/molecular mechanics (QM/MM) methodology using two-layer ONIOM method and different density functional theory (DFT) functionals in the absence of periodic boundary conditions (PBC). It was found by selecting an appropriate size for the Au surface, the results obtained using QM/MM method were in good agreement with those obtained via the periodic DFT calculations with the same functional. The calculated adsorption energies (Ead) using M06-2X and M06-L functional were in good agreement with those, recently, obtained using periodic DFT calculations considering PBC and employing van der Waals (vdW) DFT functionals. The correlation diagram between the molecular orbitals of isolated deformed AD (AD-D) and CY (CY-D) and their molecular orbitals in [email protected] and [email protected] systems have also been investigated in this work.