[QE-users] CASTEP to QE setup parameters conversions

[Husak Michal]

You are probably right

trust_radius_min have identical default numeric value in QE as geom_disp_tol in CASTEP

It is probably max tolerable displacement in Angestrem :

>From QE manual:

Minimum ionic displacement in the structural relaxation
BFGS is reset when trust_radius<https://www.quantum-espresso.org/Doc/INPUT_PW.html#trust_radius> < trust_radius_min<https://www.quantum-espresso.org/Doc/INPUT_PW.html#trust_radius_min>.
(bfgs only)



I hope reset = go to next SCF cycle ...

Funny   trust_radius<https://www.quantum-espresso.org/Doc/INPUT_PW.html#trust_radius>  is mentioned in the formula but its meaning is not described in the manual ...

________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Yuvam Bhateja <yuvamb16 at gmail.com>
Sent: Saturday, November 14, 2020 9:13:50 PM
To: Quantum ESPRESSO users Forum
Subject: Re: [QE-users] CASTEP to QE setup parameters conversions

I haven't used CASTEP, but from the description you mentioned, trust_radius_max/min is same. BFGS relaxation converge/finish when total force and change in total energy is below forc_conv_thr and etot_conv_thr. Through trust radius you can adjust what can be the max, min and initial atomic displacement system will make in each BFGS cycle to achieve converge.

On Sun, 15 Nov 2020, 1:37 am Husak Michal, <Michal.Husak at vscht.cz<mailto:Michal.Husak at vscht.cz>> wrote:
> First of all, you can find all the information about units of data in pw.x input manual.

For conv_thr the units are missing in the manual (but is is probably (a.u.)


>Regarding the ecutrho, it is a very important factor for any DFT calculation,

ecutrho equivalent is impossible to find in any CASTEP manual mot in related materials.

I will ask CASTP developers directly ...


According trust_radius_max - there is not clear description in manual how it works,  In manual is only written

"

Maximum ionic displacement in the structural relaxation.
(bfgs only)
"

Does it mean  BFGS runs until all shifts are less than this criteria ?

________________________________
From: users <users-bounces at lists.quantum-espresso.org<mailto:users-bounces at lists.quantum-espresso.org>> on behalf of Yuvam Bhateja <yuvamb16 at gmail.com<mailto:yuvamb16 at gmail.com>>
Sent: Saturday, November 14, 2020 8:44:25 PM
To: Quantum ESPRESSO users Forum
Subject: Re: [QE-users] CASTEP to QE setup parameters conversions

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<mailto:Michal.Husak at vscht.cz><mailto:Michal.Husak at vscht.cz<mailto: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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