[QE-users] CASTEP to QE setup parameters conversions

[Andrii Shyichuk]

Hear Mihal,

 From my experience with CASTEP, it's defining difference are the 
pseudopotentials.
Thus, if you want to replicate a CASTEP calculation - use the CASTEP 
UPFs as well.
Even on-the-fly runs create UPFs in the project folder (at least via 
Materials Studio).

However, I am not a fan of that potentials, and I have my reasons.
I was doing a fairly similar calculation with both CASTEP and QE (manual 
finite displacement force estimation).
With CASTEP, I was getting some weird differences in energies where 
there should have been none.
With QE, there was no such problem.

Just for a general impression, compare default cutoffs for lanthanides 
with 4f as valence electrons:
in CASTEP, its 340 eV; in PSLibrary, it's about 1500 eV.
So, either CASTEP authors found a way to reproduce the fine structure of 
4f orbitals with fewer plane waves, or their potentials are, well, not 
quite good.
I am not trying to hurt anyone, but this particular aspect is 
suspicious.
Not sure if that transfers to other elements as well.

Best regards.
Andrii Shyichuk, University of Wrocław.

W dniu 2020-11-14 20:51, Husak Michal napisał:
> Dear Nicola Marzari
> 
> 
> I had already done everything you suggest + more:
> 
> 1) Converted my structures by the Material Cloud convertor
> 
> 2) Converted my structures by BURAI GUI
> 
> 3)Semi/manually converted my structures from CIF to QE by the help of 
> QE
> 
> internal Space Group Handling
> 
> 4) Read multiple articles optimizing QE parameters exactly for the
> same problem I investigate (organic molecular crystals)
> 
> + tested the parameters they use (e.g.
> https://pubs.acs.org/doi/10.1021/cg4002797 )
> 
> 
> I know how to process my data in QE ..
> 
> I search for maximally exact CASTEP/QE calculations setup replication,
> 
> to be able to check performance/result of both codes ...
> 
> I had already made huge  number of calculations in CASTEP optimizing
> the setup/performance ..
> 
> So I ask how to set QE identically as CASTEP as much as possible ...
> 
> 
> 
> 
> 
> ________________________________
> From: Nicola Marzari <nicola.marzari at gmail.com>
> Sent: Saturday, November 14, 2020 8:22:48 PM
> To: Quantum ESPRESSO users Forum; Husak Michal
> Subject: Re: [QE-users] CASTEP to QE setup parameters conversions
> 
> 
> One possibility would be to upload your structure (or in principle even
> your CASTEP .cell file) here:
> https://www.materialscloud.org/work/tools/qeinputgenerator
> 
> This will give you fairly reliable input parameters (cutoff, sampling,
> etc...) and pseudopotentials for a scf calculation,
> and then try to understand from this document
> https://www.quantum-espresso.org/Doc/INPUT_PW.html
> what else you need
> 
>              nicola
> 
> 
> On 14/11/2020 20:13, Husak Michal 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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> 
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