Competition between Pauli Exclusion and H‑Bonding: H₂O and NH₃ on Silicene

We demonstrate that the competition between Pauli exclusion and H-bonding dominates the adsorption of H₂O on silicene through first-principles calculations. It explains the bewildering problem that isolated H₂O is inert on silicene while isolated NH₃ tends to chemisorption. Moreover, Pauli exclusion can be overcome by the synergetic effect of Si···O dative bonding and intermolecular H-bonding. As a result, H₂O molecules are readily to chemisorb in clusters. It is expected that the competition is in general polar molecule adsorption on silicene and, thus, crucial for the adsorption mechanism