[QE-users] CASTEP to QE setup parameters conversions

[Yuvam Bhateja]

Hey Michal,

First of all, you can find all the information about units of data in pw.x
input manual. And yes, you can change the units and use, keep in mind about
convergence criteria, QE uses total force where as some DFT codes uses max
force present on a single atom.

Regarding the ecutrho, it is a very important factor for any DFT
calculation, some programs have different name, for example in SIESTA it is
meshcuttoff. Please refer to input manual for detailed info of all
parameters, it can be helpful.

For your geom_disp_tol in CASTEP, you can check trust_radius_(min/max/ini)
which offers the same purpose.

All the energy units are in Rydberg, as mentioned in manual.

Hope it helps.
I am also facing similar problems by going from QE to SIESTA.

Keep in touch

Regards
Yuvam

On Sun, 15 Nov 2020, 12:43 am Husak Michal, <Michal.Husak at vscht.cz> wrote:

> Hi all
>
>
> I was working a lot with CASTEP last years ...
>
> I want to switch some my projects to  QE + do head to head comparison with
> CASTEP.
>
> I am confused by some selected corresponding setup parameters conversion
>
> (I had handled the rest including input formats conversion myself):
>
>
> QE: etot_conv_thr  (a.u.]
>
> CASTEP: geom_energy_tol (eV/atom)
>
> Should I simply  recalculate eV to a.u. and multiply by number of atoms in
> unit cell ?
>
> Why the definition in QE/CASTEP differs ?
>
>
> QE: forc_conv_thr  (a.u.)
>
> CASTEP: geom_force_tol (eV/angstrem)
>
> I have no idea how to convert this  parameter ....
>
>
> QE: non existing criteria
>
> CASTEP: geom_disp_tol (angstrem) , Maximal atom displacement during a
> cycle ..
>
> Sound like QE does not check this criteria ?
>
>
> QE: ecutrho (Ry), default 4 * ecutwfc
>
> CASTEP: non existing parameter
>
> Any idea why CASTEP does not use this parameter ?
>
>
> QE: conv_thr  , units not found/missing in manual, probably (a.u.) ?
>
> CASTEP: elec_energy_tol (eV/atom)
>
> Should I simply  recalculate eV to a.u. and multiply by number of atoms in
> unit cell ?
>
> Why the definition differs ?
>
>
> Michal Husak
>
> UCT Prague, Department of Solid State Chemistry
>
>
>
>
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