Structural, electronic, dynamical, and superconducting properties in dense GeH ₄(H ₂) ₂

Hydrogen-rich materials have fascinating physical and chemical properties such as various structures and superconductivity under high-pressure. In this study, structural, electronic, dynamical, and superconducting properties of GeH ₄(H ₂) ₂ are investigated based on the first-principles calculations. We first predict several phase transitions of GeH ₄(H ₂) ₂ under pressure. Below 28 GPa, two degenerated structures with I4̄m2 and Pmn2 ₁ symmetries are preferred, which can be viewed as the distortion of the experimentally observed fcc structure. Then, the GeH ₄(H ₂) ₂, via a triclinic phase that stabilizes in the pressure range of 28-48 GPa, transforms into a metallic orthorhombic phase in which appears the metallization induced by pressure. Another metallic phase with P2 ₁/c symmetry enters the phase diagram at around 220 GPa, which is more stable than the case of a decomposed material, and its stability is also confirmed by including the zero point energy correction. In the high-pressure P2 ₁/c phase, the superconductivity is found, and the superconducting transition temperature is predicted to be as high as 76-90 K at 250 GPa. This superconductivity mainly results from the local vibrations of more H ₂ units, though the vibration of Ge in an H ₂-formed grid also contributes to the electron-phonon interaction. This study is helpful for understanding the superconducting mechanism on hydrogen-rich compounds. © 2012 American Chemical Society.