Molecular alignment descriptor to search for the most stable adsorption sites of saturated cyclic compounds on metal surfaces

Abstract

We propose a new descriptor, called degree of molecular alignment (DMA), which can facilitate identification of the most stable adsorption configurations of saturated cyclic compounds. It exploits the binding phenomenon by lower axial CH bond activation on a metal surface. To validate this descriptor, seven saturated cyclic compounds were chosen to be adsorbed on Pd(111) and Pt(111) surfaces and confirmed that DMA was linearly related to adsorption energy. Isosurfaces of the charge density difference for the most stable adsorption configuration appeared perpendicularly, which means that good molecular alignment (parallel ring to surface) is important for the binding interaction. Moreover, origin of the differences in adsorption behaviors between Pd(111) and Pt(111) such as sensitivity towards values of DMA is studied by calculating bonding and deformation energies. The results revealed that differences in lattice parameters of catalyst induce adsorbates to have unique degree of deformation leading to different variation of bonding energy and adsorption energy with respect to values of DMA. Our result will provide a useful guideline to search for the most stable adsorption configurations of saturated cyclic compounds on metal surfaces.