<div dir="ltr">Dear Stefano,<div><br></div><div>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.</div><div><br></div><div>I hope my question is clear.</div><div>Thanks so much!</div><div><br></div><div>All the best,</div><div>Martina</div><div><br></div>Martina Lessio<br>Postdoctoral Research Scientist<br>Department of Chemistry<br>Columbia University<div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Apr 24, 2018 at 10:53 AM, Martina Lessio <span dir="ltr"><<a href="mailto:ml4132@columbia.edu" target="_blank">ml4132@columbia.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Dear Stefano,<div><br></div><div>Thank you very much for your prompt response, that helps a lot!</div><div>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.</div><div><br></div><div>All the best,</div><div>Martina</div></div><div class="gmail_extra"><div><div class="h5"><br><div class="gmail_quote">On Tue, Apr 24, 2018 at 3:23 AM, Stefano de Gironcoli <span dir="ltr"><<a href="mailto:degironc@sissa.it" target="_blank">degironc@sissa.it</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<p><tt>Dear Martina Lessio,</tt></p>
<p><tt> 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.<br>
</tt></p>
<p><tt> coming to the way things converge:</tt></p>
<p><tt> - total energy convergence with respect to ecutwfc is
expected to be from above </tt><tt><tt>because of variational
principle</tt>: 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.<br>
</tt></p>
<p><tt> - 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.<br>
</tt></p>
<p><tt> - 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.</tt></p>
<p><tt> hope this helps<br>
</tt></p>
<p><tt>stefano</tt><br>
</p><div><div class="m_6004932123691587237h5">
<br>
<div class="m_6004932123691587237m_-3203274337787247819moz-cite-prefix">On 24/04/2018 05:56, Martina Lessio
wrote:<br>
</div>
</div></div><blockquote type="cite"><div><div class="m_6004932123691587237h5">
<div dir="ltr">Dear Quantum Espresso community,
<div><br>
</div>
<div>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.</div>
<div>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):</div>
<div><img src="cid:part1.2D2DD99A.A75EBD52@sissa.it" width="545" height="327"><br>
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.</div>
<div>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.</div>
<div><br>
</div>
<div>Thank you so much!</div>
<div><br>
</div>
<div>Kind Regards,</div>
<div>Martina Lessio</div>
<div>
<div><br>
</div>
<div class="m_6004932123691587237m_-3203274337787247819gmail_signature">
<div dir="ltr">
<div dir="ltr">
<div>Postdoctoral Research Scientist</div>
<div>Department of Chemistry</div>
<div>Columbia University</div>
<br>
<p><span style="font-variant-ligatures:no-common-ligatures"> &control</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">
calculation = 'scf'</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">
restart_mode='from_scratch',</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">
prefix='MoTe2_ecutwfc',</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">
pseudo_dir =
'/home/mlessio/espresso-5.4.0/<wbr>pseudo/',</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">
outdir='/home/mlessio/espresso<wbr>-5.4.0/tempdir/'</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures"> /</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures"> &system</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">
ibrav= 4, A=3.530, B=3.530, C=13.882, cosAB=-0.5,
cosAC=0, cosBC=0,</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">
nat= 6, ntyp= 2,</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">
ecutwfc =60.0 ecutrho=300.</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">
nspin =4, lspinorb =.true., noncolin=.true.</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures"> /</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures"> &electrons</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">
mixing_mode = 'plain'</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">
mixing_beta = 0.7</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">
conv_thr = 1.0d-8</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures"> /</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">ATOMIC_SPECIES</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures"> Mo
95.96 Mo.rel-pbe-spn-rrkjus_psl.1.0.<wbr>0.UPF</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures"> Te
127.6 Te.rel-pbe-n-rrkjus_psl.1.0.0.<wbr>UPF</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">ATOMIC_POSITIONS
{crystal}</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">Te
0.333333334 0.666666643
0.625000034</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">Te
0.666666641 0.333333282
0.375000000</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">Te
0.666666641 0.333333282
0.125000000</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">Te
0.333333334 0.666666643
0.874999966</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">Mo
0.333333334 0.666666643
0.250000000</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">Mo
0.666666641 0.333333282
0.750000000</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures"></span><br>
</p>
<p><span style="font-variant-ligatures:no-common-ligatures">K_POINTS
{automatic}</span></p>
<p><span style="font-variant-ligatures:no-common-ligatures">
8 8 2 0 0 0</span></p>
</div>
</div>
</div>
</div>
</div>
<br>
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<br>
</div></div><pre>______________________________<wbr>_________________
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</blockquote>
<br>
</div>
<br>______________________________<wbr>_________________<br>
users mailing list<br>
<a href="mailto:users@lists.quantum-espresso.org" target="_blank">users@lists.quantum-espresso.o<wbr>rg</a><br>
<a href="https://lists.quantum-espresso.org/mailman/listinfo/users" rel="noreferrer" target="_blank">https://lists.quantum-espresso<wbr>.org/mailman/listinfo/users</a><br></blockquote></div><br><br clear="all"><div><br></div></div></div><span class="HOEnZb"><font color="#888888">-- <br></font></span><div class="m_6004932123691587237gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><span class="HOEnZb"><font color="#888888">Martina Lessio, Ph.D.<div>Frontiers of Science Lecturer in Discipline</div></font></span><span class=""><div>Postdoctoral Research Scientist</div><div>Department of Chemistry</div><div>Columbia University</div></span></div></div></div></div>
</div>
</blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr">Martina Lessio, Ph.D.<div>Frontiers of Science Lecturer in Discipline</div><div>Postdoctoral Research Scientist</div><div>Department of Chemistry</div><div>Columbia University</div></div></div></div></div>
</div>