Structures and phase transitions of ScH3 under high pressure.

The structures and the phase transitions of ScH3 under high pressure are investigated using first-principles calculations. The calculated structural parameters at zero pressure agree well with the available experimental data. With increasing pressure, the transition sequence hcp (GdH3-type)→C2/m→fcc→hcp (YH3-type) →Cmcm of ScH3 is predicted first; the corresponding transition pressures at 0 K are 23 GPa, 25 GPa, 348 GPa, and 477 GPa, respectively. The C2/m symmetry structure is a possible candidate but not a good one as the intermediate state from hexagonal to cubic in ScH3. On the other hand, via the analysis of the structures of hexagonal ScH2.9, cubic ScH3, and cubic ScH2, we find that the repulsive interactions of H-H atoms must play an important role in the transition from hexagonal to cubic. [ABSTRACT FROM AUTHOR]