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The nature of the interaction of tris-(8-hydroxyquinoline) aluminum (Alq3) with the Mg(001) surface is investigated by means of the van der Waals density functional. We show that there are strong chemical bonds between adsorbate O and substrate Mg atoms. The bonding energy is, however, cancelled out by the energy required to distort the molecule and the surface upon adsorption. The van der Waals (vdW) interaction between the ligand and the surface stabilizes the chemisorption state. Our study clarifies the subtle interplay between covalent bonds, vdW attraction, and structural distortion. |
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