Energy Decomposition Analysis for Metal Surface–Adsorbate Interactions by Block Localized Wave Functions

The
energy decomposition analysis based on block localized wave
functions (BLW-EDA) allows one to gain physical insight into the nature
of chemical bonding, decomposing the interaction energy in (1) a “frozen”
term, accounting for the attraction due to electrostatic and dispersion
interactions, modulated by Pauli repulsion, (2) the variationally
assessed polarization energy, and (3) the charge transfer. This method
has so far been applied to gas- and condensed-phase molecular systems.
However, its standard version is not compatible with fractionally
occupied orbitals (i.e., electronic smearing) and, as a consequence,
cannot be applied to metallic surfaces. In this work, we propose a
simple and practical extension of BLW-EDA to fractionally occupied
orbitals, termed Ensemble BLW-EDA. As illustrative examples, we have
applied the developed method to analyze the nature of the interaction
of various adsorbates on Pt(111), ranging from physisorbed water to
strongly chemisorbed ethylene. Our results show that polarization
and charge transfer both contribute significantly at the adsorption
minimum for all studied systems. The energy decomposition analysis
provides details with respect to competing adsorption sites (e.g.,
CO on atop vs hollow sites) and elucidates the respective importance
of polarization and charge transfer for the increased adsorption energy
of H2S compared to H2O. Our development will
enable a deeper understanding of the impact of charge transfer on
catalytic processes in general.