DFT investigation of CO adsorption on Pt(211) and Pt(311) surfaces from low to high coverage.

Adsorption of CO on Pt(211) and Pt(311) surfaces has been investigated by the density functional theory (DFT) method (periodic DMol3) with full geometry optimization. Adsorption energies, structures, and C-O stretching vibrational frequencies are studied by considering multiple possible adsorption sites and comparing them with the experimental data. The calculated C-O stretching frequencies agree well with the experimental ones, and precise determination of adsorption sites can be carried out. For Pt(211), CO adsorbs at the atop site on the step edge at low coverage, but CO adsorbs at the atop and bridge sites simultaneously on both the step edge and the terrace with further increasing CO coverage. The present results interpret the reflection adsorption infrared (RAIR) spectra of Brown and co-workers very well from low to high coverage. For Pt(311), CO adsorbs also at the atop site on the step edge at low coverage. The lifting of reconstruction by CO adsorption occurs also for Pt(311), whereas the energy gain for lifting the reconstruction of the Pt(311) surface is smaller than that for Pt(110). The largest difference between the stepped Pt(211)/Pt(311) and Pt(110) surfaces is the occupation on the edge sites at higher coverage. For the stepped surfaces, the bridge site begins to be occupied at higher coverage, whereas the atop site is always occupied for the Pt(110) surface.