DFT insights into the bonding mechanism of five-membered aromatic heterocycles containing N, O, or S on Fe(110) surface

Understanding the interaction of five-membered aromatic heterocycles with Fe(110) surface is crucial for the development of novel inhibitors against the corrosion of iron and steel. Herein, we report a detailed study of the adsorption properties and the bonding mechanism of pyrrole, furan, and thiophene on Fe(110) surface employing density functional theory (DFT) calculations. In the most stable adsorption geometries, we found that the adsorbates lie flat at the hollow site and form chemical bondings with four Fe atoms on Fe(110) surface. The chemisorptions are indicated by large adsorption energies and charge transfers from the surface to the adsorbates. We also found that taking into account vdW corrections in the DFT calculations has a minimal effect on the adsorption geometries whereas it significantly increases the adsorption energies. The energetic and structural analysis reveals large molecular distortions induced by the adsorbate-surface interactions, and among the adsorbates, thiophene experiences the least molecular distortion, thereby having the largest adsorption energy. The electronic structure analysis also reveals that the nature of electronic interaction of pyrrole, furan, and thiophene with Fe(110) surface is due to the strong overlaps of the frontier  and * orbitals of the adsorbates with Fe-3dz2 and Fe-(3dxz+3dyz) states of the surface. The charge donation and back-donation between the adsorbates and Fe(110) surface were also elucidated by the Bader charge analysis and the charge density difference.