Hydrogenated Silicon Fullerenes: Effects of H on the Stability of Metal-Encapsulated Silicon Clusters

Ab initio calculations of H interaction on ${\mathrm{S}\mathrm{i}}_{12}M$, ${\mathrm{S}\mathrm{i}}_{18}{M}_2$ ($M=\mathrm{C}\mathrm{r}$, Mo, and W), and $\mathrm{Z}\mathrm{r}@{\mathrm{S}\mathrm{i}}_{16}$ fullerene ($f$) show relatively weak binding of H in agreement with experimental results of H free ${\mathrm{S}\mathrm{i}}_{12}M$ and ${\mathrm{S}\mathrm{i}}_{18}{M}_2$ clusters. Adsorption of H enhances $s{p}^3$ bonding between the Si atoms, weakens the $M\mathrm{\text{−}}\mathrm{S}\mathrm{i}$ cage interactions, and leads to distortions in the cages. $\mathrm{S}{\mathrm{i}}_{\mathrm{12}}{\mathrm{C}\mathrm{r}\mathrm{H}}_{12}$ has $4{\mu }_B$ magnetic moment in contrast to zero for ${\mathrm{S}\mathrm{i}}_{12}\mathrm{C}\mathrm{r}$. Removal of the $M$ atom leads to stable empty cages of $\mathrm{S}{\mathrm{i}}_{\mathrm{12}}{\mathrm{H}}_{\mathrm{12}}$, $f\mathrm{\text{−}}\mathrm{S}{\mathrm{i}}_{\mathrm{16}}{\mathrm{H}}_{\mathrm{16}}$, and $f\mathrm{\text{−}}\mathrm{S}{\mathrm{i}}_{\mathrm{20}}{\mathrm{H}}_{\mathrm{20}}$ with large highest occupied–lowest unoccupied molecular orbital gaps of 2.5–3.0 eV, making them attractive for optoelectronic applications.

Figure 1

Optimized structures of (a) ${\mathrm{S}\mathrm{i}}_{12}M{\mathrm{H}}_{12}$, $M=\mathrm{M}\mathrm{o}$, W, and Hf; (b) $\mathrm{S}{\mathrm{i}}_{\mathrm{12}}\mathrm{C}\mathrm{r}{\mathrm{H}}_{\mathrm{12}}$; (c) H on W site of $\mathrm{S}{\mathrm{i}}_{\mathrm{12}}\mathrm{W}$; (d) $\mathrm{S}{\mathrm{i}}_{\mathrm{13}}\mathrm{M}\mathrm{o}$; (e) ${\mathrm{S}\mathrm{i}}_{18}{M}_2$, $M=\mathrm{M}\mathrm{o}$, and W; (f) an isomer of $\mathrm{S}{\mathrm{i}}_{\mathrm{18}}{\mathrm{W}}_{\mathrm{2}}$; (g) $\mathrm{S}{\mathrm{i}}_{\mathrm{17}}{\mathrm{W}}_{\mathrm{2}}$; (h),(i) isomers of $\mathrm{S}{\mathrm{i}}_{\mathrm{17}}{\mathrm{W}}_{\mathrm{2}}$; (j) $\mathrm{S}{\mathrm{i}}_{\mathrm{24}}\mathrm{C}{\mathrm{r}}_{\mathrm{3}}$; (k) $\mathrm{S}{\mathrm{i}}_{\mathrm{30}}\mathrm{C}{\mathrm{r}}_{\mathrm{4}}$; (l) H on the W site of $\mathrm{S}{\mathrm{i}}_{\mathrm{18}}{\mathrm{W}}_{\mathrm{2}}$; (m) H on a Si site of $\mathrm{S}{\mathrm{i}}_{\mathrm{18}}{\mathrm{W}}_{\mathrm{2}}$; (n) $\mathrm{S}{\mathrm{i}}_{\mathrm{18}}{\mathrm{W}}_{\mathrm{2}}{\mathrm{H}}_{12}$; (o) $\mathrm{S}{\mathrm{i}}_{\mathrm{18}}\mathrm{C}{\mathrm{r}}_{\mathrm{2}}{\mathrm{H}}_{12}$. Red balls represent H atoms while the $M$ atom is yellow, green, or blue. Si-Si bonds with lengths less than $2.6\AA$ are connected.

Figure 2

Two views of the isosurfaces of spin polarization for $\mathrm{S}{\mathrm{i}}_{\mathrm{12}}\mathrm{C}\mathrm{r}{\mathrm{H}}_{\mathrm{12}}$ (a),(b) and $\mathrm{S}{\mathrm{i}}_{\mathrm{18}}\mathrm{C}{\mathrm{r}}_{\mathrm{2}}{\mathrm{H}}_{12}$ (c),(d) with the value of 0.004.

Figure 3

Optimized structures of (a) $\mathrm{S}{\mathrm{i}}_{\mathrm{16}}\mathrm{Z}\mathrm{r}{\mathrm{H}}_{\mathrm{8}}$ (H on eight square Si atoms), (b) $\mathrm{S}{\mathrm{i}}_{\mathrm{16}}\mathrm{Z}\mathrm{r}{\mathrm{H}}_{\mathrm{8}}$ (H on eight ring Si atoms), (c) $\mathrm{S}{\mathrm{i}}_{\mathrm{16}}\mathrm{Z}\mathrm{r}{\mathrm{H}}_{\mathrm{16}}$, (d) $\mathrm{S}{\mathrm{i}}_{\mathrm{12}}{\mathrm{H}}_{\mathrm{12}}$, (e) ${\mathrm{S}{\mathrm{i}}_{\mathrm{16}}\mathrm{H}}_{16}$, and (f) ${\mathrm{S}{\mathrm{i}}_{\mathrm{20}}\mathrm{H}}_{20}$.