Vibrational Recognition of Adsorption Sites for Carbon Monoxide on Platinum and Platinum-Ruthenium Surfaces

TL;DR

This study uses density-functional perturbation theory to accurately predict vibrational frequencies of CO on platinum and platinum-ruthenium surfaces, aligning well with experimental data and analyzing the chemical origins of frequency shifts.

Contribution

It demonstrates the effectiveness of density-functional calculations in predicting vibrational frequencies and analyzes the chemical factors influencing frequency shifts on transition metal surfaces.

Findings

Calculated frequencies agree with spectroscopic measurements.

Frequency shifts due to ruthenium monolayers are correctly predicted.

Density-functional methods accurately predict vibrational frequencies despite limitations in adsorption energy predictions.

Abstract

We have studied the vibrational properties of CO adsorbed on platinum and platinum-ruthenium surfaces using density-functional perturbation theory within the Perdew-Burke-Ernzerhof generalized-gradient approximation. The calculated C-O stretching frequencies are found to be in excellent agreement with spectroscopic measurements. The frequency shifts that take place when the surface is covered with ruthenium monolayers are also correctly predicted. This agreement for both shifts and absolute vibrational frequencies is made more remarkable by the frequent failure of local and semilocal exchange-correlation functionals in predicting the stability of the different adsorption sites for CO on transition metal surfaces. We have investigated the chemical origin of the C-O frequency shifts introducing an orbital-resolved analysis of the force and frequency density of states, and assessed the effect of donation and backdonation on the CO vibrational frequency using a GGA + molecular U approach. These findings rationalize and establish the accuracy of density-functional calculations in predicting absolute vibrational frequencies, notwithstanding the failure in determining relative adsorption energies, in the strong chemisorption regime.