Assessing Vibrational Frequencies of CO Adsorbed on Cerium Oxide Surfaces Using SCAN and r2SCAN Functionals

TL;DR

This study evaluates the effectiveness of SCAN and r2SCAN meta-GGA functionals compared to HSE06 hybrid functional in predicting CO vibrational frequencies on cerium oxide surfaces, highlighting the limitations of meta-GGA approaches.

Contribution

It provides a comparative analysis of meta-GGA functionals versus hybrid DFT for surface vibrational frequency predictions, emphasizing the importance of hybrid functionals for accuracy.

Findings

Meta-GGA functionals do not significantly improve predictions over GGA for oxidized surfaces.

Adding Hubbard U improves charge localization but not vibrational frequency accuracy.

Hybrid DFT remains necessary for reliable interpretation of experimental vibrational data.

Abstract

The vibrational frequency of carbon monoxide (CO) adsorbed on ceria-based catalysts serves as a sensitive probe for identifying exposed surface facets, provided that experimental reference data on well-defined single-crystal surfaces and reliable theoretical assignments are available. Previous studies have shown that the hybrid DFT approach using the HSE06 functional yields good agreement with experimental observations, whereas the generalized gradient approximation (GGA) with PBE+U does not. In this work, we assess the performance of different exchange-correlation functionals by comparing the meta-GGA functionals SCAN and r2SCAN meta-GGA functionals with HSE06 in predicting CO vibrational frequencies on cerium oxide surfaces. The meta-GGA functionals offer no significant improvement for oxidized CeO2(111) and CeO2(110) surfaces and fail to localize excess charge on the reduced surfaces. Adding a Hubbard U term improves charge localization, but the predicted vibrational frequencies still fall short of HSE06 accuracy. These limitations are attributed to the meta-GGA's inability to adequately capture facet- and configuration-specific donation and back-donation effects, which influence the C-O bond length and CO force constant upon adsorption. Despite the higher computational cost when used with plane-wave basis sets, hybrid DFT remains essential for accurate interpretation of experimental results.