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<p><tt>Dear Martina Lessio,</tt></p>
<p><tt> the 8*ecutwfc is a rule of thumb that is indeed often
suggested for US pseudopotential.</tt></p>
<p><tt> There is nothing special in the factor 8, it simply
reflects the expectation that </tt><tt><tt>augmentation charges
typically contain more Fourier components than the 4*ecutwfc
coming from the square of the wavefuncitons. <br>
</tt>
</tt></p>
<p><tt> </tt></p>
<p><tt> As you did the converge test and found that 55/280 Ry are
good in your case it should be ok to use these values.</tt></p>
<p><tt> best,<br>
</tt></p>
<p><tt>stefano</tt><br>
</p>
<br>
<div class="moz-cite-prefix">On 25/04/2018 22:11, Martina Lessio
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAGco_WQw8zW=daF9N9+1DkH20Ek3Bo5Ys6kxUZ-3ju3V7yOxEA@mail.gmail.com">
<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"
moz-do-not-send="true">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"
moz-do-not-send="true">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:part3.DDF4FFC2.2F17DDA3@sissa.it"
class="" 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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<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>
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