[QE-users] optimization under pressure

[Lorenzo Paulatto]

> Is it sufficient for structural optimization under a certain pressure?

yes

> What algorithm does QE apply during pressure application? 

whatever algorithm you choose (default is bfgs)

> does it use symmetry in calculations? 

yes

> If QE uses symmetry, the force and stress 
> calculated under the symmetry condition prevent the transition to 
> another mesh.

no, more specifically:

The code will keep the symmetry of the crystal (lattice+basis), not that 
of the lattice alone. Furthermore, the cell may rotate in a way that 
makes it impossible to represent it with the same choice of ibrav 
afterward. This is only a problem in less symmetric systems.

You can prevent the rotation by choosing cell_dofree="ibrav" (which will 
make the relax slightly less efficient) or you can rotate the cell back 
at the end, using the scan_ibrav.x utility from PW/tools (the current 
development version is much faster and more accurate than the python 
version of QE 6.0 -> 6.5). I recommend using atomic positions in crystal 
coordinates in this case.

cheers


> thank you for help and suggestions.
> 
> best regards,
> Tahsin
> 
> 
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-- 
Lorenzo Paulatto - Paris