Structural optimization at different pressures

[RicardoCecconello]

Dear Dr. Tadano,

I'm investigating a material's second-order phase transition and would like to check a few things regarding the structural optimization performed with ALAMODE on the SCPH level. More precisely, I'd like to investigate the dependency of the phase transition temperature on the pressure.

1. What is the more suitable approach for pressure scanning?

• Should we calculate the IFCs for a phase optimized at each pressure and then perform the structural optimization for a temperature range? or
• Is it sufficient to use RELAX_STR=2 and specify a pressure with STAT_PRESSURE, with the same IFCs calculated for the structure at 0 GPa?

2. It is said in the tutorial on BaTiO3 structural optimization that the IFCs need to be the ones of the phase with the highest symmetry. In my case, that phase is unstable at 0 GPa. So should we calculate the IFCs for this phase on a pressure where it is stable, and use this result for other pressures?