Novel Structures and Superconductivity of Silane under Pressure

Following the suggestion that hydrogen-rich compounds, and, in particular, silane (SiH4), might be high-Tc 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 P21/c and I41/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 Tc of 16 K. Our calculations also show that the imaginary phonons of the recently proposed P63 generate the Pbcn structure.