Novel descriptors based on density functional theory for predicting divalent metal ions adsorbed onto silica-disiloxane cluster model study

The optimized structures and equilibrium energies of metal aquo-complexes binding with disiloxane ((SiH3)20*) cluster model on silica surface are studied using the local (Vosko-Wilk-Nusair) and nonlocal (Becke-Perdew-Wang) density functional theory methods. The divalent Mg, Ca, Sr, Ba, Zn, Cd and Hg metal ions are investigated. The results show that the structures of silica surface cluster and adsorbed metal aquo-ion have obvious changes after the adsorptive reaction carried out, especially for the case of inner-sphere adsorption. The atomization energy of metal aquo-ion/disiloxane cluster binding complexes (AE(o); AE(i)) and the inverse of metal-oxide bond length of metal aquo-ions (R-MO(-1)) can be used to supply two novel descriptors for accurately predicting the stability constant (log K-int j.k,) of the surface complexation model for divalent metal ions adsorbed on silica in aqueous solutions. However, if the commonly used parameters such as the calculated energy changes (DeltaE(o); DeltaE(i)) in the binding reactions of disiloxane cluster model + aqueous metal ion --> aqueous metal ion/disiloxane cluster binding complexes are employed to succeed the role of previous atomization energies as the predicting descriptors, it is found that the liner regression results are inferior to the previous results predicted by using the atomization energies. (C) 2003 Elsevier B.V. All rights reserved.