[QE-users] Potential issue with charge density cutoff convergence and K-point grid convergence
Martina Lessio
ml4132 at columbia.edu
Fri Apr 27 18:18:46 CEST 2018
Dear Giuseppe,
Thanks so much for the clarification. Now understand Jia's point and I will
definitely look into trying norm conserving pseudo for my system.
Thank you all for your numerous responses and help!
All the best,
Martina
On Thu, Apr 26, 2018 at 3:04 AM, Giuseppe Mattioli <
giuseppe.mattioli at ism.cnr.it> wrote:
>
> Dear Martina
> If you look at Jia’s comment from the other side, a norm conserving pseudo
> might be OK with a 80/320 Ry cutoff (ONCV PPs from the sg15 library usually
> are). And you get rid of all the usual limitations of US (e.g. slow or
> unstable calculations with hybrid EXX functionals).
> HTH
> Giuseppe
>
> Martina Lessio <ml4132 at columbia.edu> ha scritto:
>
> Dear Jia,
>>
>> Thanks so much for your feedback. I see your point, although that is the
>> result I got from my convergence tests. Perhaps I will have another look
>> at
>> my tests and check that I have not been too conservative with selecting
>> the
>> parameters. Furthermore the suggested minimum cutoff for one of the pseudo
>> potentials I am using is 50 Ry so I don't think I can go much lower than
>> that.
>>
>> All the best,
>> Martina
>>
>> On Wed, Apr 25, 2018 at 5:23 PM, Jia Chen <jiachenchem at gmail.com> wrote:
>>
>> Dear Martina,
>>>
>>> If I may interject, the advantage of ultrasoft pseudopotentail is not
>>> using wavefunction cutoff as large as 55 Ry. Usually ultrasoft and norm
>>> conserving pseudopotential have similar density cutoff, but ultrasoft
>>> only
>>> need about half the wavefunction cutoff.
>>>
>>> Cheers
>>> Jia
>>>
>>> On Wed, Apr 25, 2018 at 4:11 PM, Martina Lessio <ml4132 at columbia.edu>
>>> wrote:
>>>
>>> Dear Stefano,
>>>>
>>>> I have one more question regarding the convergence tests. I have
>>>> performed the tests in the order that you recommended and found that if
>>>> I
>>>> set ecutrho=280 Ry I can get away with ecutwfc=55 Ry without negatively
>>>> impacting the convergence. So I am thinking of using these parameters
>>>> for
>>>> my future calculations. However, I have read in many QE resources that
>>>> if
>>>> you use ultrasoft pseudopotentials like I do, ecutrho should be at least
>>>> equal to 8*ecutwfc. So I am now wondering whether it is an issue that
>>>> in my
>>>> case ecutrho is only equal to about 5*ecutwfc or given that I performed
>>>> the
>>>> recommended convergence tests it is okay to have this setup even for
>>>> pseudopotentials.
>>>>
>>>> I hope my question is clear.
>>>> Thanks so much!
>>>>
>>>> All the best,
>>>> Martina
>>>>
>>>> Martina Lessio
>>>> Postdoctoral Research Scientist
>>>> Department of Chemistry
>>>> Columbia University
>>>>
>>>>
>>>> On Tue, Apr 24, 2018 at 10:53 AM, Martina Lessio <ml4132 at columbia.edu>
>>>> wrote:
>>>>
>>>> Dear Stefano,
>>>>>
>>>>> Thank you very much for your prompt response, that helps a lot!
>>>>> I will repeat the tests as you suggested but it's good to know that my
>>>>> system is behaving normally and I can then proceed with more complex
>>>>> calculations.
>>>>>
>>>>> All the best,
>>>>> Martina
>>>>>
>>>>> On Tue, Apr 24, 2018 at 3:23 AM, Stefano de Gironcoli <
>>>>> degironc at sissa.it
>>>>> > wrote:
>>>>>
>>>>> Dear Martina Lessio,
>>>>>>
>>>>>> first of all I would say that a convergence error of 1.d-5 Ry in a
>>>>>> 6
>>>>>> atom cell looks pretty much converged to me. I think that even your
>>>>>> ecutrho
>>>>>> = 240 Ry calculation (~1.d-5 Ry per atom) looks quite good.
>>>>>>
>>>>>> coming to the way things converge:
>>>>>>
>>>>>> - total energy convergence with respect to ecutwfc is expected to
>>>>>> be
>>>>>> from above because of variational principle: the higher ecutwfc is the
>>>>>> more planewaves are included in the wavefunction expansion, hence the
>>>>>> lower
>>>>>> the energy. However in the ultrasoft pseudopotential definition the
>>>>>> energy
>>>>>> is not only a function of the wavefunctions but also includes a
>>>>>> dependence
>>>>>> on augmentation charges, that are localized and may contain higher
>>>>>> Fourier
>>>>>> components with respect to 4*ecutwfc ( = 240 in your case). Failing to
>>>>>> include enough Fourier components in the augmentation charges will
>>>>>> affect a
>>>>>> number of integrals but not in a variational way... integrals would
>>>>>> simply
>>>>>> be inaccurate and the inaccuracy can be both from above or from below.
>>>>>>
>>>>>> - I would perform cutoff convergence test in a slightly different
>>>>>> order: 1) I would check convergence of total energy (and stress, and
>>>>>> forces) as a function of ecutwfc using the default value for
>>>>>> ecutho=4*ecutwfc (that is without specifying ecutrho in the input).
>>>>>> When
>>>>>> this procedure converges (and it can initially converge from below
>>>>>> due to
>>>>>> augmentation charge Fourier components being missing) this means that
>>>>>> wavefunction expansion AND augmentation-charge expansion are both
>>>>>> converged. 2) I would then fix ecutrho=4*converged_ecutwfc, which
>>>>>> takes
>>>>>> care of augmentation charge convergence, and I would check whether I
>>>>>> can
>>>>>> get away with a lower ecutwfc for the wavefunction expansion.
>>>>>>
>>>>>> - as for k-point sampling convergence, there is no variational
>>>>>> principle w.r.t. number of k-points: it's again a matter of
>>>>>> convergence of
>>>>>> an integral. The denser the grid the better the integral but there is
>>>>>> no
>>>>>> variational principle with respect to which k-point you include and
>>>>>> which
>>>>>> you dont.
>>>>>>
>>>>>> hope this helps
>>>>>>
>>>>>> stefano
>>>>>>
>>>>>> On 24/04/2018 05:56, Martina Lessio wrote:
>>>>>>
>>>>>> Dear Quantum Espresso community,
>>>>>>
>>>>>> I am new to Quantum Espresso and I am trying to run some simple
>>>>>> simulations on MoTe2 bulk. Unfortunately I seem to be having some
>>>>>> issues
>>>>>> with some preliminary convergence tests for charge density cutoff and
>>>>>> K-point grid and I am hoping to get some help from you on this.
>>>>>> Here is a graph with the results of the charge density cutoff
>>>>>> convergence test I performed while setting the kinetic energy cutoff
>>>>>> equal
>>>>>> to 60 Ry (I performed a test to set this as well):
>>>>>>
>>>>>> I am worried about these results because I would expect the total
>>>>>> energy to go down rather than going up when I increase ecutrho. I also
>>>>>> observe a similar energy trend when I increase the k-point grid,
>>>>>> which also
>>>>>> seems unusual and possibly wrong to me.
>>>>>> I am copying below the input I have used for these calculations and I
>>>>>> would greatly appreciate any help with figuring our whether I am doing
>>>>>> something wrong.
>>>>>>
>>>>>> Thank you so much!
>>>>>>
>>>>>> Kind Regards,
>>>>>> Martina Lessio
>>>>>>
>>>>>> Postdoctoral Research Scientist
>>>>>> Department of Chemistry
>>>>>> Columbia University
>>>>>>
>>>>>> &control
>>>>>>
>>>>>> calculation = 'scf'
>>>>>>
>>>>>> restart_mode='from_scratch',
>>>>>>
>>>>>> prefix='MoTe2_ecutwfc',
>>>>>>
>>>>>> pseudo_dir = '/home/mlessio/espresso-5.4.0/pseudo/',
>>>>>>
>>>>>> outdir='/home/mlessio/espresso-5.4.0/tempdir/'
>>>>>>
>>>>>> /
>>>>>>
>>>>>> &system
>>>>>>
>>>>>> ibrav= 4, A=3.530, B=3.530, C=13.882, cosAB=-0.5, cosAC=0,
>>>>>> cosBC=0,
>>>>>>
>>>>>> nat= 6, ntyp= 2,
>>>>>>
>>>>>> ecutwfc =60.0 ecutrho=300.
>>>>>>
>>>>>> nspin =4, lspinorb =.true., noncolin=.true.
>>>>>>
>>>>>> /
>>>>>>
>>>>>> &electrons
>>>>>>
>>>>>> mixing_mode = 'plain'
>>>>>>
>>>>>> mixing_beta = 0.7
>>>>>>
>>>>>> conv_thr = 1.0d-8
>>>>>>
>>>>>> /
>>>>>>
>>>>>> ATOMIC_SPECIES
>>>>>>
>>>>>> Mo 95.96 Mo.rel-pbe-spn-rrkjus_psl.1.0.0.UPF
>>>>>>
>>>>>> Te 127.6 Te.rel-pbe-n-rrkjus_psl.1.0.0.UPF
>>>>>>
>>>>>> ATOMIC_POSITIONS {crystal}
>>>>>>
>>>>>> Te 0.333333334 0.666666643 0.625000034
>>>>>>
>>>>>> Te 0.666666641 0.333333282 0.375000000
>>>>>>
>>>>>> Te 0.666666641 0.333333282 0.125000000
>>>>>>
>>>>>> Te 0.333333334 0.666666643 0.874999966
>>>>>>
>>>>>> Mo 0.333333334 0.666666643 0.250000000
>>>>>>
>>>>>> Mo 0.666666641 0.333333282 0.750000000
>>>>>>
>>>>>>
>>>>>> K_POINTS {automatic}
>>>>>>
>>>>>> 8 8 2 0 0 0
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> users mailing listusers at lists.quantum-espresso.orghttps://
>>>>>> lists.quantum-espresso.org/mailman/listinfo/users
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> users mailing list
>>>>>> users at lists.quantum-espresso.org
>>>>>> https://lists.quantum-espresso.org/mailman/listinfo/users
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Martina Lessio, Ph.D.
>>>>> Frontiers of Science Lecturer in Discipline
>>>>> Postdoctoral Research Scientist
>>>>> Department of Chemistry
>>>>> Columbia University
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> Martina Lessio, Ph.D.
>>>> Frontiers of Science Lecturer in Discipline
>>>> Postdoctoral Research Scientist
>>>> Department of Chemistry
>>>> Columbia University
>>>>
>>>> _______________________________________________
>>>> users mailing list
>>>> users at lists.quantum-espresso.org
>>>> https://lists.quantum-espresso.org/mailman/listinfo/users
>>>>
>>>>
>>>
>>> _______________________________________________
>>> users mailing list
>>> users at lists.quantum-espresso.org
>>> https://lists.quantum-espresso.org/mailman/listinfo/users
>>>
>>>
>>
>>
>> --
>> Martina Lessio, Ph.D.
>> Frontiers of Science Lecturer in Discipline
>> Postdoctoral Research Scientist
>> Department of Chemistry
>> Columbia University
>>
>
>
> GIUSEPPE MATTIOLI
> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
> Via Salaria Km 29,300 - C.P. 10
> I-00015 - Monterotondo Scalo (RM)
> Mob (*preferred*) +39 373 7305625
> Tel + 39 06 90672342 - Fax +39 06 90672316
> E-mail: <giuseppe.mattioli at ism.cnr.it>
>
>
> _______________________________________________
> users mailing list
> users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
>
--
Martina Lessio, Ph.D.
Frontiers of Science Lecturer in Discipline
Postdoctoral Research Scientist
Department of Chemistry
Columbia University
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20180427/785316bb/attachment.html>
More information about the users
mailing list