Structural and electronic phase transitions ofThS2from first-principles calculations

Abstract

Thorium and its compounds have received considerable attention in recent years due to the renewed interest in developing the thorium fuel cycle as an alternative nuclear energy technology. There is pressing current need to explore the physical properties essential to the fundamental understanding and practical application of these materials. Here we report on a computational study of thorium disulfide (ThS2), which plays an important role in the thorium fuel reprocessing cycle. We have employed the density functional theory and evolutionary structure search methods to determine the crystal structures, electronic band structures, phonon dispersions and density of states, and thermodynamic properties of ThS2 under various pressure and temperature conditions. Our calculations identify several crystalline phases of ThS2 and a series of structural phase transitions induced by pressure and temperature. The calculated results also reveal electronic phase transitions from the semiconducting state in the low-pressure phases of ThS2 in the P nma and F m3m symmetry to the metallic state in the high-pressure phases of ThS2 in the P nma and I4/mmm symmetry. These results explain the experimental observation of the thermodynamic stability of the P nma phase of ThS2 at the ambient conditions and a pressure-induced structural phase transition in ThS2 around 40 GPa. Moreover, the present study reveals considerable additional information on the structural and electronic properties of ThS2 in a wide range of pressure and temperature. Such information provides key insights into the fundamental material behavior and the underlying mechanisms that lay the foundation for further exploration and application of ThS2.

First-principles study of pressure-induced phase transitions, mechanical and thermodynamic properties of ThBC

“…At high pressures, the calculations for ThC 2 show that the polymerization behavior of C atoms is increasing with increasing pressures [25]. The crystal structural, electronic, and thermodynamic properties of ThS 2 were studied at various pressures [26]. Our calculations show that the Fm 3m phase of ThS 2 is energetically (23 meV/f.u.)…”

Ab initio study on crystal structure and phase stability of ZrC2 under high pressure*

“…The structural predications of the global free energy minimization of ZrC 2 were performed using the CALYPSO code [22] based on the PSO methodology, [16] which has been proved to be effective in predicting the structure of various materials. [23][24][25][26][27][28][29] The ionic position, volume and shape of the structure cell were allowed to vary in their structural relaxations. The Brillouin-zone (BZ) of P2 1 /c, P4 2 /nmc, Immm, P6/mmm, Cmc2 [30] for the primitive cell of ZrC 2 .…”

Pressure-induced structural transformations and polymerization in ThC2

“…The free energy global minimization of ThC 2 were performed by merging ab initio total energy calculations and particle-swarm optimization algorithm19 on structural predictions, as implemented in the CALYPSO code20. It has been proven to be effective and accurate in predicting the crystal structures of a large variety of materials444546474849505152. The structural relaxations were performed allowing the variations of the ionic position, cell volume, and cell shape.…”