<div dir="ltr"><div><div><div><div><div><div><div><div><div><div><div><div>Dear Stefano, <br><br></div>Thank you for you fast reply. <br><br></div>Thank you for the suggestions. I will look into those routine to place a perturbation a lift the degeneracies. <br><br></div>But before that, just to be sure. <br></div>Would it make sense to compare the wavefunction if we look at a non-degenerate band. For example the first one in diamond is non degenerate throughout the BZ. <br><br></div>Then, there is the degeneracy due to symmetries. The WF a one k-point could be any linear combination of the WF at the other k-points related by symmetry. <br><br></div>Would it be possible to lift that degeneracy by removing the symm (nosym=.true. and noinv = .true.)? <br></div>In that case I could compare the wf?<br><br></div>In passing, while looking into that, I found a bug PW/src/init_us_2.f90<br><br></div>At the beginning of the routine the out variable vkb_ should be initialized<br>vkb_(:, :) = (0.d0,0.d0)<br><br></div>I had some NaN due to that and adding the zeroing solved it. <br><br></div>Best, <br><br></div>Samuel <br><div><div><div><div><br><div><div><div><div><div><br><br><div><div><div><div><br><br><br><div><br><br></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On 31 October 2015 at 19:17, 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">
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<div>On 31/10/2015 19:45, Samuel Poncé
wrote:<br>
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<div>Dear all, <br>
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I would like to present the
following test:<br>
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1) Diamond with the normal 48 sym
(incl frac translation)<br>
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VS<br>
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2) Diamond where the code is tricked
into having two different type of atom
with two psp (24 sym & no frac
translation). The two psp are the same
with a different name. <br>
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The input files are join to this email
(first I do a scf calc followed by a
nscf calc where I put by hand all the
kpoints). <br>
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The two case should in theory give exactly
the same physical observable. <br>
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wavefunctions are not physical observables.<br>
<br>
random global phases appear due to numerical noise, random
non-global phases appear among degenerate wavefunctions.<br>
<br>
my suggestion is to formulate your problem in a gauge invariant
way... <br>
which should be the only thing that make sense physically.<br>
<br>
If you insist in attaching a meaning to a specific wavefunction you
should use a guiding function to fix the phases and break the tie
caused by degeneracy.<br>
<br>
I think you could use some concepts developed to align wfcs in
neighboring points in Wannier functions construction (either in the
Wannier90 code or in the PP/src/poormanwannier.f90 tool) and/or in
the band-tracking bit coded in PP/src/bands.f90<br>
<br>
stefano <br>
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However, when I print the ground state WF
summed on G-vectors and bands for each
k-points: SUM(evc(:,:)) where the evc dim
are evc(npw,nbnd).<br>
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I get for the first case:<br>
ik 1<br>
SUM(evc)
(0.524554603771020,-0.985842296616562)<br>
ik 2<br>
SUM(evc)
(-0.210256090577016,0.545845252785036)<br>
ik 3<br>
SUM(evc)
(-0.239028680198133,-1.83612435123587)<br>
ik 4<br>
SUM(evc)
(-0.565218210001339,-0.820699742516653)<br>
ik 5<br>
SUM(evc)
(1.42454745428565,-0.957929628317023)<br>
ik 6<br>
SUM(evc)
(-0.274745448323905,1.09643888529245)<br>
ik 7<br>
SUM(evc)
(-0.933074272062335,1.16077508535444)<br>
ik 8<br>
SUM(evc)
(0.989923346231570,-1.58533060259471)<br>
ik 9<br>
SUM(evc)
(-1.26782798392043,-0.150960156635521)<br>
ik 10<br>
SUM(evc)
(-0.401891345164427,1.27585476000084)<br>
.......<br>
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For the second case<br>
ik 1<br>
SUM(evc) (0.116807098229033,-1.11058471838606)<br>
ik 2<br>
SUM(evc) (-0.215236454279303,0.546415812538992)<br>
ik 3<br>
SUM(evc) (-0.239955952913802,-1.83623414069791)<br>
ik 4<br>
SUM(evc)
(-0.566091061918831,-0.820097940655045)<br>
ik 5<br>
SUM(evc) (1.42304578433157,-0.960163474240552)<br>
ik 6<br>
SUM(evc) (-0.281026989151429,1.09416630115645)<br>
ik 7<br>
SUM(evc) (-0.933137702445232,1.16063633276210)<br>
ik 8<br>
SUM(evc) (0.989188453055074,-1.58571465239844)<br>
ik 9<br>
SUM(evc) (-1.26782806755424,-0.150960132814025)<br>
ik 10<br>
SUM(evc) (-0.401891332187340,1.27585476604143)<br>
<br>
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You can see that their norm is well the same but
for some k-point the phase is exactly the same
whereas for other k-point the phase is strongly
different. <br>
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<div>I must also add that the values that are
different cannot be found at other k-point in the
other example. It is therefore not a problem of
k-ordering. <br>
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This lead to a problem for me because I try to look
at <br>
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<\Psi_k+q| might be something here or not
|\psi_k>. <br>
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Therefore if the k are the same but the k+q point happen
to have a phase difference, such phase does not cancels
out. <br>
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Is there a way to impose to have the same phase for the
two case or a maximum have a global phase that does not
depend on the k-point?<br>
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Best Regards, <br>
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Samuel Ponce<br>
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