Crystal structures and properties of the CH4H2 compound under high pressure
Abstract
The structural, electronic, and dynamical properties and intermolecular interactions of CH4H2 are investigated based on first-principles calculations. Enthalpy calculations indicate that the P structure is the most stable phase below 15.6 GPa. On compression, the P212121 phase possesses the lowest enthalpy, then the P21/C becomes energetically favorable above 98.2 GPa. The pressure-induced hardening behavior of H2-bonds in the CH4H2 system reproduces the experimental data well. In addition, the CH4 molecules remain as tetrahedra due to the weak interactions of molecular H2 and CH4. At higher pressure, the orientation of H2 molecules in CH4H2 is also disordered and this resembles the findings for pure H2. It shows that comparing to pure H2, the addition of CH4 does not have much limitations on the rotation of the H2 molecules.