[Pw_forum] hybrid functionals: dexx<0
Matteo Gerosa
mgerosa88 at gmail.com
Fri Nov 29 19:25:46 CET 2013
Dear Giuseppe,
Indeed I tried with different exxdiv_treatment methods except the one which allows to manually set the ecutvcut cutoff (vcut_ws), since I read somewhere that it can be useful only in the case of strongly anisotropic cells and in non-bulk systems. I can try though. Instead I didn't try with different PPs, that's a good idea. Thanks for your help!
Ciao,
Matteo
> Il giorno 29/nov/2013, alle ore 19:01, Giuseppe Mattioli <giuseppe.mattioli at ism.cnr.it> ha scritto:
>
>
> Dear Matteo
> Did you also try to play a bit with different exxdiv_treatment methods
> (with different ecutvcut cutoffs) and/or different PPs?
> Ciao
> Giuseppe
>
> Quoting Matteo Gerosa <mgerosa88 at gmail.com>:
>
>> Dear Giuseppe,
>>
>> thanks for your answer. I'm using the 5.0.2 version of QE plus 5.0.3
>> patches. I'm running bulk calculations on MgO (rocksalt structure). The
>> problem arises only for some q-grids (in one case, also when setting the
>> q-grid equal to the k-grid), but I haven't understood why. And, as I said
>> before, shifting the k-grid alone solves the problem. I attach here a
>> sample input file.
>>
>> &CONTROL
>> calculation = 'scf' ,
>> restart_mode = 'from_scratch' ,
>> outdir = '/home/matteo/qe/tmp/' ,
>> pseudo_dir = '/home/matteo/qe/espresso-5.0.2/pseudo/' ,
>> prefix = 'mgo_hse06' ,
>> verbosity = 'default' ,
>> tstress = .true. ,
>> tprnfor = .true. ,
>> /
>> &SYSTEM
>> ibrav = 2,
>> celldm(1) = 7.9594,
>> nat = 2,
>> ntyp = 2,
>> ecutwfc = 100.0 ,
>> nbnd = 8 ,
>> input_dft = 'hse', nqx1 = 2, nqx2 = 2, nqx3 = 2,
>> x_gamma_extrapolation = .true.,
>> exxdiv_treatment = 'gygi-baldereschi',
>> /
>> &ELECTRONS
>> conv_thr = 1.0d-9 ,
>> mixing_beta = 0.7 ,
>> /
>> &IONS
>> ion_dynamics = 'bfgs' ,
>> /
>> ATOMIC_SPECIES
>> Mg 24.30500 Mg.pbe-hgh.UPF
>> O 15.99940 O.pbe-mt.UPF
>> ATOMIC_POSITIONS alat
>> Mg 0 0 0
>> O 0.5 0.5 0.5
>> K_POINTS automatic
>> 4 4 4 0 0 0
>>
>>
>> Thank you for your help.
>>
>> Matteo
>>
>>
>>
>> 2013/11/29 Giuseppe Mattioli <giuseppe.mattioli at ism.cnr.it>
>>
>>>
>>> Dear Matteo
>>> Which QE version are you using?
>>> I've clashed against similar issues, introduced in the late svn
>>> versions and (probably) corrected in the latest version, which were
>>> not present in the stable 5.0.2 version. If you are using the stable
>>> version, the problem should come out only in the case of strongly
>>> anisotropic (e.g., surface slabs with large vacuum) cells. Do you find
>>> it in bulk simulations (ZnO and TiO2, I suppose...:-))?. I've
>>> performed EXX simulations of these two guys, in the case of bulk as
>>> well as of surface cells. I did not fall into your dexx errors.
>>> HTH
>>>
>>> Giuseppe
>>>
>>> Giuseppe Mattioli
>>> ISM-CNR
>>> Italy
>>>
>>> Quoting Matteo Gerosa <mgerosa88 at gmail.com>:
>>>
>>>> Dear all,
>>>>
>>>> I've been trying to calculate band gaps for some semiconductor oxides
>>>> using hybrid functionals (pbe0, hse, b3lyp).
>>>> I've learned the choice of the q-grid for computing the exchange energy
>>>> can be critical. Indeed in some cases I cannot achieve self-consistency
>>>> and an error message appears in the output file warning that the dexx
>>>> correction term becomes negative.
>>>> I guess this is related to the small-q divergence issue for some
>>>> particular q-grid patterns. In fact, if the k-grid is shifted away from
>>>> gamma (keeping the q-grid fixed) convergence is achieved. Unfortunately,
>>>> this doesn't allow me to compute the gap at the gamma point, which I'm
>>>> interested in. On the other hand, I also obtain convergence if I set
>>>> "x_gamma_extrapolation=.false.", but this induces large errors for a
>>>> small number of points in the q-grid.
>>>> How is it possible to solve the problem and, more importantly, predict
>>>> in which configurations of the q-grid could the problem arise? Is there
>>>> any way to shift the q-grid away from gamma?
>>>>
>>>> Thanks for any help you can provide.
>>>>
>>>> Best regards,
>>>>
>>>> Matteo Gerosa
>>>>
>>>> --
>>>> Matteo Gerosa
>>>> NanoLab - Micro and Nanostructured Materials Lab
>>>> Department of Energy, Politecnico di Milano
>>>> Via Ponzio 34/3 I-20133 Milano, Italy
>>>>
>>>> tel. +39 02 2399 6364
>>>> web: www.nanolab.polimi.it
>>>>
>>>>
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>>>
>>>
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>>> Giuseppe Mattioli
>>> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
>>> v. Salaria Km 29,300 - C.P. 10
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>
> --
> ********************************************************
> - Article premier - Les hommes naissent et demeurent
> libres et ègaux en droits. Les distinctions sociales
> ne peuvent être fondèes que sur l'utilitè commune
> - Article 2 - Le but de toute association politique
> est la conservation des droits naturels et
> imprescriptibles de l'homme. Ces droits sont la libertè,
> la propriètè, la sùretè et la rèsistance à l'oppression.
> ********************************************************
>
> Giuseppe Mattioli
> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
> v. Salaria Km 29,300 - C.P. 10
> I 00015 - Monterotondo Stazione (RM)
> Tel + 39 06 90672836 - Fax +39 06 90672316
> E-mail: <giuseppe.mattioli at ism.cnr.it>
>
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