An investigation of on the properties of Pt-based surface alloys via computational QM methods

Abstract

The adsorption properties of CO on stepped Pt3Sn(102) surface were investigated using quantum mechanical calculations. The two possible terminations of experimentally verified stepped surface, Pt3Sn (102), were generated and on these terminations all types of possible adsorption sites were determined. The adsorption energies and geometries of the CO molecule for all those sites were calculated. The most favorable sites for adsorption were determined as the short bridge site between SE and TA atoms of pure Pt row on the mixed atom ending termination, atop site on SE atom of the pure row of pure-Pt ending termination and atop site on SE atom of the pure row of the mixed atom ending termination. The results were compared with those for similar sites on the flat Pt3Sn(110) surface considering the fact that Pt3Sn(102) has terraces with (110) orientation. The adsorption energies of stable sites on Pt3Sn(102) surface are in general larger than those of the similar sites on Pt3Sn(110) surface. The difference in adsorption energies of those sites is a result of stepped structure of Pt3Sn(102). Aiming to understand the interactions between the adsorbate and surface metal atoms present at the adsorption sites in detail, the local density of states (LDOS) of the adsorbent Pt and C of adsorbed CO was utilized. The LDOS of the surface metal atoms with CO adsorbed atop and of its clean state were compared to see the effect of CO chemisorption on the electron distribution of the corresponding Pt atom. The downward shift in energy peak in the LDOS curves as well as changes in the electron densities of the corresponding energy levels indicate the orbital mixing between CO molecular orbitals and metal d states. The studies clearly showed that the adsorption strength of the sites has a direct relation with their LDOS profiles.