[QE-users] Error received when applying non-hydrostatic pressure at vc-relax

[mkondrin]

On 16.07.2021 10:59, Arif Emre Yarimbiyik wrote:
> Hi,
>
> I am trying to calculate the electronic structure of semiconducting
> crystals such as GaAs under pressure. The flow that I am applying is:
> - optimize the geometry with vc-relax, where I enter the desired pressure
> at 'press'
> - use the resulting structure at electronic band structure calculation with
> a hybrid functional such as HSE06.
> There's no problem when I apply hydrostatic pressure, but when I try to
> apply directional pressure I receive errors. I do this by using cell_dofree
>
> &CELL
>    cell_dynamics='damp-w',
>    press=10.d0,
>    press_conv_thr=0.5d0,
>    cell_dofree = 'x',
> /
Hi,

AFAIK you can not simply apply pressure along x-axis this way. For 3D 
materials we have such a feature as Poisson's ratio, so pressure applied 
along one direction develops stress in directions normal to it.

I would suggest using cell_dofree='yz' press=0.0 options and use not 
optimal cell parameters but compressed by say 1% in x direction. This 
would result in uniderectional pressure the value of which will be 
calculated in the course of vc-relax procedure.

Sincerely yours,
M.V. Kondrin
>
> Specificly my problem falls into the following at the QE troubleshooting
> file:
>
> ---5.0.0.27 pw.x stops during variable-cell optimization in checkallsym
> with non orthogonal operation error---
>
> One of the advised solutions is to "use a symmetry-conserving algorithm:
> the Wentzcovitch algorithm (cell dynamics='damp-w') should not break the
> symmetry." , which I tried without success.
>
> I would greatly appreciate an alternative solution to the problem.
>
> Best Regards,
>
> Emre Yarımbıyık
>
>
>
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