First-principle applications on protonated adenine dimers with N-H⋯N intermolecular coupling

The geometry structures and the electronic properties of protonated adenine dimer were described employing the first-principle hybrid density functional theory with a special emphasis on N-H⋯N hydrogen bond coupling mode complexes. Nine stable isomers with N-H⋯N type H-bonds were characterized on its potential energy surface and classified as planar and nonplanar two types. The optimized geometry and the Mulliken charge populations indicate that the spontaneous proton transfer occurs in some isomers owning to strong N-H⋯N coupling. The stabilization energies corrected with the basis set superposition error (EBSSE) and zero-point vibrational energy (ZPVE) demonstrate the following significant points. First, the impact factors of EBSSE, such as geometry structure, the number of H-bonds, and proton situation, are proposed. Second, the dimers with the N1′-H15′⋯N type H-bonds are more stable than others. Third, the whole system should be included to analyze the stability of the dimer.