Calculating Enthalpy and Entropic Effects on phase-stability

[paulfons]

I have a system in which there are two possible phases, a room-temperature stable phase and a
high-temperature phase. The system has been experimentally observed to a phase transition from the
RT phase to the high temperature phase in a system in which there is likely considerable pressure
and elevated temperatures present due to confinement. There are experimental TEM observations of the
lattice constant of each phase in the confined system that can be used to define the unit cells of
each phase. I would like to simulate the effects of pressure and temperature on the relative
stability of the two phases. To do this, I have calculated the enthalpy of each phase as a function
of pressure using the PSTRESS keyword (at 0K). I have then gathered these results and plotted the
enthalpy of each phase with respect to applied pressure. To take into account phonon-related entropy
effects I have calculated the Gibbs free energy using phonopy-qha and the quasi-harmonic
approximation. I have then added the Helmholtz energy (TS) contributions to the enthalpy plots for a
range of temperatures. My question is simple, is this a reasonable way to investiate the relative
stability stability of the two phases?

[support_vasp]

Hi,

We're sorry that we didn’t answer your question. This does not live up to the quality of support that we aim to provide. It looks like your question is more of a general scientific one, so it may be better placed in a different forum where people have more expertise in calculating phase diagrams. The team has since expanded. If we can still help with your problem, please ask again in a new post, linking to this one, and we will answer as quickly as possible.

Best wishes,

VASP