Following the suggestion that hydrogen-rich compounds, and, in particular, silane (${\mathrm{SiH}}_4$), might be high-$T_c$ superconductors at moderate pressures, very recent experiments have confirmed that silane metallises and even becomes superconducting at high pressure. In this article, we present a structural characterization of compressed silane obtained with an ab initio evolutionary algorithm for crystal structure prediction. Besides the earlier molecular and chainlike structures of $P{2}_1/c$ and $I{4}_1/a$ symmetries, respectively, we propose two novel structures with space groups $Fdd2$ and $Pbcn$, to be stable at 25–55 and 220–250 GPa, respectively. According to our calculations, silane becomes metallic and superconducting at 220 GPa in the layered $Pbcn$ structure, with a theoretical $T_c$ of 16 K. Our calculations also show that the imaginary phonons of the recently proposed $P{6}_3$ generate the $Pbcn$ structure.

• Received 16 September 2008

DOI:https://doi.org/10.1103/PhysRevLett.102.087005