Molecular shape and the energetics of chemisorption: From simple to complex energy landscapes

TL;DR

This study systematically analyzes the energy landscape of rigid adsorbates on surfaces, revealing how molecular size and shape influence the number of minima, binding energy variation, and surface mobility, with implications for molecular recognition.

Contribution

It provides a comprehensive enumeration of local minima for model molecules on surfaces and elucidates how molecular size and registry affect adsorption energetics and surface interactions.

Findings

Number of energy minima increases linearly with molecular size.

Incommensurate molecules exhibit larger variations in minima positions.

Higher registry molecules show faster decrease in binding energy variation.

Abstract

We enumerate all local minima of the energy landscape for model rigid adsorbates characterized by three or four equivalent binding sites (e.g., thiol groups) on a close-packed (111) surface of a face-centered-cubic crystal. We show that the number of energy minima increases linearly with molecular size with a rate of increase that depends on the degree of registry between the molecule shape and the surface structure. The sparseness of energy minima and the large variations in the center-of-mass positions of these minima vs molecular size for molecules that are incommensurate with the surface suggests a strong coupling in these molecules between surface mobility and shape or size fluctuations resulting from molecular vibrations. We also find that the variation in the binding energy with respect to molecular size decreases more rapidly with molecular size for molecules with a higher degree of registry with the surface. This indicates that surface adsorption should be better able to distinguish molecules by size if the molecules are incommensurate with the surface.