[QE-users] vc-relax

[Lorenzo Paulatto]

> thank you very much for your answer, i try it.but i set 
> cell_dofree='2Dxy' , because i need to fix cell parameter. in z direct.
> 
We recently noticed that the BFGS default algorithm does not always 
respect the cell_dofree constraint, a fix is in the developmenet verison 
of the code but not in the released version.

As a workaround you can take the bfgs_module.f90 file from the 
development version
https://gitlab.com/QEF/q-e/raw/develop/Modules/bfgs_module.f90
and overwrite the one you find in Modules// and recompile the code.

Or you can set
ion_dynamics = 'damp'
and
cell_dynamics = "damp-pr"
which should respect the constraint.

That said, there is no specific problem to use cell_dofree='ibrav' in 
conjunction with another cell_dofree, I just implemented this feature as 
a cell_dofree value because of lazyness.

You can open Modules/cell_base.f90 and at line 84 change
LOGICAL   :: enforce_ibrav = .FALSE.! True if ibrav ...
to
LOGICAL   :: enforce_ibrav = .TRUE.! True if ibrav ...
(do not forget to recompile pw.x) to use cell_dofree="ibrav" together 
with any other cell_dofree

hth

-- 
Lorenzo Paulatto - Paris