Water adsorption on Ti-doped silicon clusters

Abstract

Ab initio calculations have been performed on adsorption of ${\mathrm{H}}_{2}\mathrm{O}$ molecules on Ti-doped silicon clusters $\mathrm{Ti}{\mathrm{Si}}_{n}$ using the ultrasoft pseudopotential method within the generalized gradient approximation. Our results show that for $n=13$ and larger clusters adsorption of ${\mathrm{H}}_{2}\mathrm{O}$ on $\mathrm{Ti}{\mathrm{Si}}_{n}$ could be difficult due to low binding energies. All these clusters have cage structures with the metal atom surrounded by the silicon atoms. On the other hand, smaller clusters with $n<13$ have the metal atom partially covered by Si atoms in a basket structure so that it is available for reaction with a water molecule. This leads to significantly higher binding energies of a water molecule on such clusters. These results are in excellent agreement with the available experimental data, which show significant decrease of ${\mathrm{H}}_{2}\mathrm{O}$ adsorption on clusters with $n>12$.