Figure 1

(a) The energetically most favorable structures computed for ${\mathrm{SiH}}_4$ in the pressure range 0–160 GPa. The golden spheres are silicon atoms and green are hydrogen atoms. (b) Enthalpies per ${\mathrm{SiH}}_4$ unit of the most important silane structures are plotted as functions of pressure. The enthalpies are referenced to that of $\mathbf{T}\mathbf{1}$. Observe for $\mathbf{O}\mathbf{2}$ the ${\mathrm{SiH}}_2$ planes resemble closely the ${\mathrm{CuO}}_2$ planes in the high-$T_c$ cuprate superconductors. A puckered variant of this square net occurs in $\mathbf{O}\mathbf{3}$, the most stable structure over a large pressure range under consideration.Reuse & Permissions

Figure 2

Structural and dimensional features of $\mathbf{O}\mathbf{1}$, $\mathbf{O}\mathbf{3}$ and $\mathbf{T}\mathbf{3}$ under pressure. (a) The structure of $\mathbf{O}\mathbf{1}$ at 0 GPa viewed a little off the [001] direction. H atoms from different adjacent unit cells form octahedral cages, shown in green. In the inset is the chain of octahedra viewed from the side. (b) $\mathbf{O}\mathbf{1}$ at 159 GPa. At this pressure, the chains of octahedra become so distorted that they are best seen as chains of tetrahedra. (c) and (d) show the structure of $\mathbf{O}\mathbf{3}$ at 150 GPa. The red and green spheres are the H atoms, and golden spheres are Si atoms. It is clear in (c) (viewed from the [100] direction) that the H atoms form slightly puckered 2-dimensional sheets. Shown in (d) is a view of $\mathbf{O}\mathbf{3}$ along the $c$ direction with only two sheets (red and green) formed by H atoms. (e) The dodecahedral coordination around Si atoms for the $\mathbf{T}\mathbf{3}$ structure at 144 GPa. Golden dodecahedra are shown for the eight silicons on the corners of the unit cell.Reuse & Permissions

Figure 3

The band gaps are shown as functions of the radii of a free-electron sphere for structures $\mathbf{T}\mathbf{1}$, $\mathbf{T}\mathbf{2}$, $\mathbf{O}\mathbf{1}$, $\mathbf{O}\mathbf{2}$, and $\mathbf{O}\mathbf{3}$. Structure $\mathbf{O}\mathbf{3}$ is computed to be the lowest-enthalpy structure in the 25–160 GPa regime, which should become metallic at $r_s=0.83\AA$. The dotted line indicates the theoretical $r_s$ at the metallization onset ($0.88\AA$) predicted based on the Goldhammer-Herzfeld criterion, where a polarizability of $5.44{\AA }^3$ for free ${\mathrm{SiH}}_4$ is assumed [21].Reuse & Permissions