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Mulakaluri, Narasimham; Pentcheva, Rossitza; Scheffler, Matthias (2010): Coverage-Dependent Adsorption Mode of Water on Fe3O4(001): Insights from First Principles Calculations. In: Journal of Physical Chemistry C, Vol. 114, Nr. 25: S. 11148-11156
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Abstract

Using density functional theory calculations together with an on-siteCoulomb repulsion term (GGA+U), we investigate the adsorption of wateron Fe3O4(001). Starting from a single water molecule per (root 2 x root2)R45 degrees unit cell, we vary the concentration and configuration ofwater and hydroxyl groups. Isolated water molecules on the clean surfacetend to dissociate heterolytically with an OH group adsorbed on top ofan octahedral iron and a proton donated to a surface oxygen.Furthermore, oxygen defects are found to promote strongly waterdissociation. The released protons bind to distant surface oxygen tominimize the repulsive interaction between the surface OH groups. Athigher coverages, the interplay between adsorbate-adsorbate andadsorbate-substrate interactions and the formation of hydrogen bondsbetween the surface species result in a crossover to a mixed adsorptionmode where every second molecule is dissociated. The energetic trendsare related to the underlying electronic mechanisms.