Modeling of the adsorption on Cr2O3 clusters of small molecules and ions present in seawater. A preliminary non-empirical study

Abstract

Non-empirical calculations of a Cr₂O₃ unit, taken as an initial model of chromium oxide clusters, interacting with ions and (small models of) molecules present in natural seawater have been carried out. The results obtained for the isolated oxide unit show that the coupling between the unpaired 3d electrons of the two chromium atoms has a negligible influence on the charge distribution. The results concerning the adsorption show that: (i) water, methanol and formic acid are dissociated; (ii) the chlorine anion, which is not strongly adsorbed, can easily be removed from the cluster; (iii) the Mg²⁺ adsorption energy is considerably larger than that of Na⁺ and Ca²⁺; (i) the interaction energy of these cations is enhanced by Cr₂O₃ hydroxylation; () dissociated methanol and formic acid are, of all the molecules considered in this study, those having the strongest interaction energy with Cr₂O₃. In a very limited number of cases the computations were repeated for a larger cluster (Cr₄O₆), for a Cr₂O₃ cluster embedded in a set of point charges, or for a hydroxylated Cr₂O₃ unit, to study the influence of the environment on the binding energy and geometrical arrangements of the complexes.