MgIn2Se4 sous contraintes, étude des liaisons fortes et faibles, étude ab initio.

Abstract

The subject of this thesis is the study of the effect of hydrostatic pressure on the compound MgIn2Se4. In order to achieve this goal, we performed an ab-initio study based on density functional theory (DFT). The dynamic stability results show that MgIn2Se4 crystallizes at room temperature in the rhombohedral structure R¯3m. Due to the compressible nature of the studied compound, the latter undergoes several structural transformations according to the sequence of direct spinel −→ inverse spinel −→ LiTiO2 -type −→ ¯I4. The inclusion of the thermal effect, on the other hand, demonstrates that the direct spinel structure F d¯3m is metastable. Also, dynamical analysis via phonon spectra shows that only the transition to the inverse structure and from there to that of the LiTiO2 -type is favorable. Our findings also shed light on the evolution and collapse of gaps when MgIn2Se4 is subjected to pressure. Finally, the (AIM) and (NCI) approaches have also permitted to visualize the properties of the chemical bond and to provide an adequate explanation linking the interactions remaining in the compound to its behavior towards the applied pressure.