First principles calculations on the effect of pressure on SiH4(H2)2

The effect of pressure on the strength of H2 covalent bond in the molecular solid SiH4(H2)2 has been investigated using quantum molecular dynamics simulations and charge density analysis. Our calculations show, in agreement with the implications of the experimental results, that substantial elongation of H2 bond can be achieved at low pressures, with the onset of rapid changes close to 40 GPa. Model calculations show redistribution of charge from bonding to antibonding states to be responsible for the behavior. Our computed Raman spectra confirm the dynamic exchange of hydrogen atoms speculated to be operative in SiH4–D2 mixture by experiments. This exchange is shown to be a three step process driven by thermal fluctuations.