A DFT investigation of methane molecular adsorption on Pt(1 0 0)

Density functional theory with generalised gradient approximation (GGA-PW91) has been used to study the adsorption of CH4 on Pt(1 0 0) surface at a coverage of 0.25 ML in a (2 × 2) unit cell. In all calculations the CH4 and the top layer of the metal were allowed to relax. Optimised geometries and adsorption energies for CH4 on three sites, namely the top, bridge and hollow sites, are presented considering various molecular orientations with respect to the surface. The calculated geometries are in good agreement with the experimental observations. The spread of adsorption energies (from −44 meV to −59 meV) over the three sites is quite small, weakly dependent on the molecular orientation, suggesting a weak interaction between CH4 and the Pt(1 0 0) surface and a weakly corrugated surface potential of the system. The evolution of C and H local density of states (LDOS) on adsorption of the molecule at top site indicates that the orbitals of H and C become involved in bonding with metal, whereas the analysis of Pt LDOS shows that CH4 interacts chemically with the Pt surface.