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 <[email protected]> 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 <[email protected]> > 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 <[email protected]> >> 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 <[email protected] >>> > 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 >>>> [email protected]https://lists.quantum-espresso.org/mailman/listinfo/users >>>> >>>> >>>> >>>> _______________________________________________ >>>> users mailing list >>>> [email protected] >>>> 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 >> [email protected] >> https://lists.quantum-espresso.org/mailman/listinfo/users >> > > > _______________________________________________ > users mailing list > [email protected] > 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
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