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I'm not telling that one should run phonon calculations at 200 Ry. 200 Ry is to get the asymptotic behavior upon vc-relax with PseudoDojo NC PP. Then one should decrease the cutoff until the asymptotic error is around 1 meV/atom. This cutoff when you get 1
meV/atom energy error is the minimum to be used if you want <b>accurate forces to calculate phonon vibrations.</b></div>
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<br>
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Maybe you can expect less stringent cutoffs to work with non-organic crystals, but the figure below shows the behavior I get from various NC PP for the vc-relax of a molecular crystal (beta-HMX). ONCV and HGH require very large cutoffs for top accuracy, whereas
PseudoDojo needs only 90-130 Ry (converged and accurate forces -> converged mass density). Again, the verification of the pressure tensor at the verification/validation step at the end of the output of QE is a very good proxy to get an insight on force accuracy.<br>
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Xavier<br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> users <users-bounces@lists.quantum-espresso.org> on behalf of mkondrin@hppi.troitsk.ru <mkondrin@hppi.troitsk.ru><br>
<b>Sent:</b> Thursday, October 27, 2022 11:03 AM<br>
<b>To:</b> Quantum ESPRESSO users Forum <users@lists.quantum-espresso.org><br>
<b>Subject:</b> Re: [QE-users] Electron Phonon Calculation: tolerance limit for P</font>
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<div class="PlainText">Hello, Xavier! Is all these efforts (increasing ecut to 200 Ry) are just
<br>
make one to believe that frequency of acoustic modes at Gamma point is <br>
zero?<br>
<br>
Sincerely yours, <br>
M. V. Kondrin<br>
<br>
On Oct 27 2022, Bidault, Xavier wrote:<br>
<br>
>Hello Ramesh,<br>
><br>
> Norm-conserving (NC) pseudopotentials (PP) require higher energy cutoffs. <br>
> You need NC PP for electron-phonon calculations. NC PP from PseudoDojo <br>
> website are very good, at least for what I've tested on organic <br>
> materials. Then you don't need ecutrho for NC PP, which are made to work <br>
> with default ecutrho = 4 x ecutwfc.<br>
><br>
> So, you should try first to increase your cutoff, up to 200 Ry should do <br>
> the job to have the asymptotic behavior with PseudoDojo NC PP <br>
> (unfortunately, other NC PP may require much higher cutoffs to get the <br>
> asymptotic behavior). Then you can choose the cutoff where the asymptotic <br>
> error is just below 1 meV/atom.<br>
><br>
> After you do a vc-relax simulation, always check the verification step at <br>
> the end of the output. If the pressure tensor is different from the <br>
> pressure tensor of the last optimization step, then it means your cutoff <br>
> is not large enough, or your system has converging issues (initial <br>
> geometry, k-points...).<br>
><br>
> I think your forc_conv_thr of 1e-4 is good. You can tighten a little bit <br>
> etot_conv_thr to 1e-5 and press_conv_thr to 0.1 kbar.<br>
><br>
> Regards, Xavier ________________________________ From: users <br>
> <users-bounces@lists.quantum-espresso.org> on behalf of Ramesh Kumar <br>
> Kamadurai via users <users@lists.quantum-espresso.org> Sent: Thursday, <br>
> October 27, 2022 3:23 AM To: users@lists.quantum-espresso.org <br>
> <users@lists.quantum-espresso.org> Subject: [QE-users] Electron Phonon <br>
> Calculation: tolerance limit for P<br>
><br>
> Dear users I am trying to calculate el-Ph coupling constant and other <br>
> properties for a superconductor. The input file is attached. I am a bit <br>
> stuck with VC-Relax calculation as the system is not able to stabilize at <br>
> 0.0 kbar. I followed all the suggestions given in forum 1. Increased <br>
> Cut-off to maximum 2. Tried USPP,NC, Mixed and currently running with <br>
> PBE-Sol 3. Sequentially done 2 VC Relax calculation but i am not able to <br>
> sort out the issue. &CONTROL<br>
> calculation = "vc-relax"<br>
> etot_conv_thr = 4.00000e-05<br>
> forc_conv_thr = 1.00000e-04<br>
> max_seconds = 1.72800e+05<br>
> nstep = 100<br>
> outdir = "/home/sjacobs/tmp/"<br>
> prefix = "PDZ-VCRELAX"<br>
> pseudo_dir = "C:\Users\RAMESH\.burai\.pseudopot"<br>
> tprnfor = .TRUE.<br>
> tstress = .TRUE.<br>
> verbosity = "high"<br>
>/<br>
><br>
>&SYSTEM<br>
> a = 6.36512e+00<br>
> degauss = 7.34986e-03<br>
> ecutrho = 6.40000e+02<br>
> ecutwfc = 8.00000e+01<br>
> ibrav = 2<br>
> nat = 4<br>
> nosym = .FALSE.<br>
> nspin = 1<br>
> ntyp = 3<br>
> occupations = "smearing"<br>
> smearing = "marzari-vanderbilt"<br>
>/<br>
><br>
>&ELECTRONS<br>
> conv_thr = 8.00000e-10<br>
> electron_maxstep = 80<br>
> mixing_beta = 4.00000e-01<br>
> startingpot = "atomic"<br>
> startingwfc = "atomic+random"<br>
>/<br>
><br>
>&IONS<br>
> ion_dynamics = "bfgs"<br>
>/<br>
><br>
>&CELL<br>
> cell_dofree = "all"<br>
> cell_dynamics = "bfgs"<br>
> press = 0.00000e+00<br>
> press_conv_thr = 5.00000e-01<br>
>/<br>
><br>
>K_POINTS {automatic}<br>
>12 12 12 0 0 0<br>
><br>
>ATOMIC_SPECIES<br>
>Ga 69.72300 Ga.pbesol-dnl-rrkjus_psl.1.0.0.UPF<br>
>Pd 106.42000 Pd_ONCV_PBEsol-1.0.upf<br>
>Zr 91.22400 zr_pbesol_v1.uspp.F.UPF<br>
><br>
>ATOMIC_POSITIONS {crystal}<br>
>Zr 0.000000 0.000000 0.000000<br>
>Ga 0.493162 0.493162 0.493162<br>
>Pd 0.739743 0.739743 0.739743<br>
>Pd 0.246581 0.246581 0.246581<br>
><br>
>The output stress is given below<br>
>entering subroutine stress ...<br>
> total stress (Ry/bohr**3) (kbar) P= 2.67<br>
> entering subroutine stress ...<br>
> total stress (Ry/bohr**3) (kbar) P= -0.41<br>
> entering subroutine stress ...<br>
> total stress (Ry/bohr**3) (kbar) P= -0.82<br>
> entering subroutine stress ...<br>
> total stress (Ry/bohr**3) (kbar) P= 0.56<br>
> entering subroutine stress ...<br>
> total stress (Ry/bohr**3) (kbar) P= 0.13<br>
> entering subroutine stress ...<br>
> total stress (Ry/bohr**3) (kbar) P= -0.08<br>
> entering subroutine stress ...<br>
> total stress (Ry/bohr**3) (kbar) P= -0.23<br>
> entering subroutine stress ...<br>
> total stress (Ry/bohr**3) (kbar) P= -0.35<br>
> entering subroutine stress ...<br>
> total stress (Ry/bohr**3) (kbar) P= -0.50<br>
> entering subroutine stress ...<br>
> total stress (Ry/bohr**3) (kbar) P= -0.63<br>
> entering subroutine stress ...<br>
> total stress (Ry/bohr**3) (kbar) P= -0.77<br>
> entering subroutine stress ...<br>
> total stress (Ry/bohr**3) (kbar) P= -0.83 My question is What <br>
> is the optimal pressure value to avoid negative frequencies for electron <br>
> phonon calculation ? Is there any mistake in my input file ? Thanks in <br>
> advance Regards Ramesh Asst. Professor GITAM University Vizag, India<br>
><br>
><br>
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