On the HSAB based estimate of charge transfer between adsorbates and metal surfaces

Graphical abstract: Left: molecule-to-metal electron charge transfer (ΔN) is proportional to the difference between the metal's work function and molecular electronegativity. Right: correlation between the work function and explicitly DFT calculated ΔN. Highlights: ► HSAB based electron transfer parameter, ΔN, is analyzed for adsorbates on metal surfaces. ► ΔN gives reasonably estimated trends of charge transfer for atomic and molecular adsorbates. ► Adatom-metal bond strength is linearly proportional to metal-to-adatom charge transfer. ► DFT calculated adsorption energies of the N, O, and Cl adatoms on 11 different metals. ► DFT calculated work functions of low Miller index surfaces for 11 different metals. - Abstract: The applicability of the HSAB based electron charge transfer parameter, ΔN, is analyzed for molecular and atomic adsorbates on metal surfaces by means of explicit DFT calculations. For molecular adsorbates ΔN gives reasonable trends of charge transfer if work function is used for electronegativity of metal surface. For this reason, calculated work functions of low Miller index surfaces for 11 different metals are reported. As for reactive atomic adsorbates, e.g., N, O, and Cl, the charge transfer is proportional to the adatom valence times the electronegativity difference between the metal surface and the adatom, where the electronegativity of metal is represented by a linear combination of atomic Mulliken electronegativity and the work function of metal surface. It is further shown that the adatom-metal bond strength is linearly proportional to the metal-to-adatom charge transfer thus making the ΔN parameter a useful indicator to anticipate the corresponding adsorption energy trends.