A density functional theory study of thiophene and pyridine adsorption on Pt/Rh-doped Cu (100) surface

The adsorption of pyridine and thiophene molecules on clean, doped Rh-Cu (100) and Pt-Cu (100) surfaces was investigated using density functional theory calculations including van der Waals interactions (optB86b-vdW). Various Rh-Cu and Pt-Cu slabs, in which the Cu surface atoms are substituted by a monomer, dimer, and tetramer, were tested by adsorbing pyridine and thiophene molecules. The adsorption properties of these systems were examined regarding their adsorption energy, adsorption heights, electron density difference (EDD), and density of states (DOS). Our results indicate that, for the thiophene molecule, the adsorption energy was increased from 0.98 to 3.55 eV after alloying the Cu surface with an Rh tetramer. Concerning the adsorption of pyridine, the adsorption energy is increased from 0.96 to 3.06 eV after substituting the Cu atoms with an Rh tetramer. Therefore, the Rh-Cu (100) doped surface was found to be more suitable for the adsorption of thiophene and pyridine in comparison with the clean surface. Bader charge analysis shows that the charge transfer was from surface atoms to the thiophene molecule for all systems except the case of the adsorption on the Pt4-Cu (100) surface. However, concerning the adsorption of pyridine on doped surfaces, all charge transfers are moved from the surface to the molecule and attained 0.34 electron charge when the Cu atoms are substituted by Rh dimer. Furthermore, the electron density difference (EDD) calculations for doped surfaces display a charge accumulation on the thiophene molecule. The EDD confirmed the results of the charge transfer obtained for the pure and doped Cu (100) surface with Pt tetramer and Rh tetramers. The results of PDOS of four metal atoms in the top layer making a 4-fold hollow site indicate an upshift of the d orbitals, which can explain the redistribution of charge between the surface and both molecules.