Few simple rules governing hydrogenation of graphene dots

TL;DR

This study explores how hydrogen atoms bind to small graphene dots with hydrogen-terminated edges, revealing simple rules influenced by electronic effects and validated through computational methods.

Contribution

It identifies fundamental rules governing hydrogenation patterns on graphene dots, linking electronic structure to adsorption preferences using theoretical models.

Findings

Hydrogen prefers edge sites due to electronic effects.

Binding energies are consistent across different computational methods.

Simple concepts from tight-binding models explain adsorption behavior.

Abstract

We investigated binding of hydrogen atoms to small Polycyclic Aromatic Hydrocarbons (PAHs) - i.e. graphene dots with hydrogen-terminated edges - using density functional theory and correlated wavefunction techniques. We considered a number of PAHs with 3 to 7 hexagonal rings and computed binding energies for most of the symmetry unique sites, along with the minimum energy paths for significant cases. The chosen PAHs are small enough to not present radical character at their edges, yet show a clear preference for adsorption at the edge sites which can be attributed to electronic effects. We show how the results, as obtained at different level of theory, can be rationalized in detail with the help of few simple concepts derivable from a tight-binding model of the $\pi$ electrons.