Atomic structure andSiH4-H2interactions ofSiH4(H2)2from first principles

Abstract

First-principles density-functional theory (DFT) calculations are used to understand the crystal structure, bonding, and vibrational properties of the recently discovered high-pressure ${\text{SiH}}_{4}{({\text{H}}_{2})}_{2}$ compound. We find a general decrease in the frequencies of the intramolecular ${\text{H}}_{2}$ stretching modes with increasing pressure, where the tetrahedral ${\text{H}}_{2}$ exhibit markedly stronger softening than octahedral ${\text{H}}_{2}$. Our DFT results suggest a weakening of the ${\text{H}}_{2}$ bond that is explained by increased orbital overlap and electron sharing between the silane and hydrogen molecules, which also account for the unusually high hydrogen capacity of ${\text{SiH}}_{4}{({\text{H}}_{2})}_{2}$.