The ground structure and the pressure-induced structural and electronic phase transitions for for rare-earth trihydride GdH3

Abstract

The ground structure and the pressure-induced structural and electronic phase transitions for rare-earth trihydride GdH3 are investigated extensively using first-principles calculations where f electrons are considered. The P3¯c1, P63cm andP63 structure models are taken as the possible ground state structure. With a higher plane-wave basis-800 eV cutoff energy, the optimized structural parameters under CASTEP code are very close to the experimental data; furthermore, it is found that both in the ferromagnetic state and the antiferromagenic state, P63cm structure has the lowest energy, followed, in this order, by theP63 and P3¯c1 structures; but under VASP code, only liking YH3, P63 structure has the lowest energy, followed, in this order, by theP63cm and P3¯c1 structures. The standard DFT band structure calculations also show that the band structure of GdH3 is similar to that of YH3, and P63 structure has the largest band gap among the structures, GGA+U calculations only can improve the band gap of GdH3 very limitedly. So the main factors that affect the opening of the band structure of GdH3 should still be algorithms. On the other hand, under compression, GdH3 follows the pressure-induced phase transition sequence AFM P3¯c1→AFMC2/m→FM C2/m→FMfcc→FMhcp→FMCmcm. In conjunction with the phase transition sequence, the pure DFT-GGA calculations of electronic structures demonstrate that the critical pressure that makes the band gap of GdH3 close is close to the transition pressure from an intermediate phase (C2/m phase) to cubic phase. In contrast to the case of YH3, it seems that the presentation of 4f electrons doesn't make rare-earth trihydride arise any abnormality in the electronic properties and the pressure-induced phase transitions with CASTEP code.