[Pw_forum] problem hybrid pseudopotential calculations
stefano de gironcoli
degironc at sissa.it
Sat Jul 23 10:07:17 CEST 2016
dear Muhammad Adnan Saqlain,
gamma extrapolation is a way to deal with the ill defined value of
the exchange integral between wfcs at k and k+q in the limit of q->0.
if you use a truncated coulomb interaction that limit is not ill
defined.
no need to use the gamma_extrapolation option
best,
stefano
On 23/07/2016 10:00, Muhammad Adnan Saqlain wrote:
> Dear Prof Clavijo
> I am extremely sorry for my misleading title of the calculation.
> Actually, It was a cubic structure consisting of Cs, Pb and I. I
> deliberately did not put the atoms in the calculation. more over I do
> not know why the algorithm for cell movement was not copied it was
> however present in the input file.
>
> 1. If I try these two options, the
>
> vcut_spherical : appropriate for cubic and quasi-cubic supercells
> vcut_ws : appropriate for strongly anisotropic supercells, see also
> ecutvcut.
>
> the program says like this
>
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> Error in routine system_checkin (1):
> x_gamma_extrapolation cannot be used with vcut
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
> I have no idea how to fix it. Can you suggest one??
>
> 2. I have now used Q-E 5.4.0, but this version does not allow vc-relax
> option with hybrid one. why is it so? How would the band gap be
> effected if I relax the cell without hybrid scheme and then calculate
> band gap with hybrid one?
>
> 3. About the ecutoff, I deliberately used small one as these are just
> calculations not the real one.
> 4. I have cubic system, may I try q-grid like 1*2*3 or it has to be
> symmetric one?
> 5. Can you suggest more about hybrid calculations?
>
>
> On Fri, Jul 22, 2016 at 10:09 PM, Josue Itsman Clavijo Penagos
> <jiclavijop at unal.edu.co <mailto:jiclavijop at unal.edu.co>> wrote:
>
> Dear, Muhammad Adnan Saqlain, remember the user documentation for
> *exxdiv_treatment*:
>
> Specific for EXX. It selects the kind of approach to be used
> for treating the Coulomb potential divergencies at small q vectors.
>
> gygi-baldereschi : appropriate for cubic and*quasi-cubic supercells*
> vcut_spherical : appropriate for cubic and quasi-cubic supercells
> vcut_ws : appropriate for strongly anisotropic supercells, see also
> ecutvcut.
> none : sets Coulomb potential at G,q=0 to 0.0 (required for GAU-PBE)
>
> *Besides that, *I**have some observations and suggestions for you
> based in the input file you send, so you can realize why does QE
> is failing when trying to simulate your system:
>
> 1 - Check if you really need to apply smearing, since this
> technique is intended to be useful for metallic systems, and
> Anatase is cleary not a metallic system, in fact, is more a
> Wide-gap or Insulator -type system.
>
> 2 - You do want to perform a vc-relax calculation, but nothing are
> specified in the cards &IONS and &CELL. There is not cell relaxing
> algorithm specified (BFGS? MD?)
>
> 3 - The card &ATOMIC_POSITIONS shows nothing: No atoms, no cell to
> relax.
>
> 4 - In the card &SYSTEM , *ecutwfc = 40.* This, in my humble
> opinion, a very poor cutoff for a serious calculation. Do
> a ecutwfc convergence test before attempt your system.
>
> 5 - Please take in account that a hybrid calculation is VERY
> expensive in terms of computational demand, so if you set up a
> vc-relax calculation using hybrid PPS you must test if *nqx1 = 1,
> 2 or 3 really makes a difference.*
> *
> *
> *6 - For some systems, input_dft=HSE is faster than **input_dft =
> "PBE0". Check if that could be your case.*
> *
> *
> By the way, are you sure Anatase has a cubic crystal structure?
> Does XCrysden show the correct structure for your input?
>
> *Best regards, *
> *
> *
>
> Josué Clavijo, PhD.
> Assistant Professor
> Universidad Nacional de Colombia
> Departamento de Química
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org <mailto:Pw_forum at pwscf.org>
> http://pwscf.org/mailman/listinfo/pw_forum
>
>
>
>
> --
> Best Regards
> Muhammad Adnan Saqlain
>
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20160723/15fed76f/attachment.html>
More information about the users
mailing list