<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<p><tt>I think the reason of the difference is the presence of macroscopic
electric fields that makes the phonon dispersion close to gamma
non -analytic (it depends on the direction of approach to Gamma
point). Accounting for this non-anayticity is the reason why one
computes the effective charges and the dielectric matrix.</tt></p>
<p><tt>when you select the path (with matdyn.x) the code knows which
direction you are approaching Gamma and includes the non
analytic terms accordingly. you get therefore the LO-TO splitting
of modes that would be otherwise degenerate (174.65). The TO
mode stays there while the LO is shifted up to 322). The other
modes are not changed because they don't have a macroscopic
polarization.</tt></p>
<p><tt>When calculation the Dos the code does not know which
direction to adopt and does not include the LO-TO splitting ..
the TO matrix is diagonalized that have additional symmetry.
This is in principle wrong but the gamma point is just a single
point in the DoS. neighboring points and the rest of the points
in the BZ should be computed correctly. <br>
</tt></p>
<p><tt>HTH<br>
</tt></p>
<p><tt>stefano<br>
</tt></p>
<p><tt></tt><br>
</p>
<br>
<div class="moz-cite-prefix">On 15/08/2018 23:24, Jie Peng wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAJTOooG89-1gY29vkBOggdSChz4XpdjjCxgV6NxqhPKqhiptZw@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=utf-8">
<div dir="ltr">Dear QE users:
<div><br>
</div>
<div>I have been running phonon calculations of HfS2 using
quantum espresso. I followed the steps of relaxing to the
equilibrium atomic configuration using pw.x, computing
dynamical matrices on a k point mesh grid using ph.x,
producing interatomic force constant matrix using q2r.x. </div>
<div><br>
</div>
<div>Now I want to plot phonon dispersion along high symmetry
direction Gamma-M-K-Gmma in the HCP (hexagonal closed pack)
HfS2 lattice. So I used the following input file for matdyn.x:</div>
<div><br>
</div>
<div>
<div><i> &input</i></div>
<div><i> asr='crystal'</i></div>
<div><i> amass(1)=178.49,</i></div>
<div><i> amass(2)=32.065,</i></div>
<div><i> ntyp=2</i></div>
<div><i> flfrc='HfS2.fc', flfrq='HfS2.freq',
q_in_band_form=.true.,</i></div>
<div><i> /</i></div>
<div><i> 4</i></div>
<div><i> 0 0 0 40</i></div>
<div><i>0.5 -0.2887 0 40</i></div>
<div><i>0.6667 0 0 40</i></div>
<div><i>0 0 0 1</i></div>
<div><br>
</div>
<div>which gives me phonon frequencies at Gamma point as: </div>
<div><br>
</div>
<div>
<div> <i> diagonalizing the dynamical matrix ...</i></div>
<div><i><br>
</i></div>
<div><i> q = 0.0000 0.0000 0.0000</i></div>
<div><i> **************************************************************************</i></div>
<div><i> freq ( 1) = -0.000000 [THz] =
-0.000001 [cm-1]</i></div>
<div><i> ( 0.545987 -0.000000 -0.167781 -0.000000
-0.084152 -0.000000 )</i></div>
<div><i> ( 0.545987 -0.000000 -0.167781 -0.000000
-0.084152 -0.000000 )</i></div>
<div><i> ( 0.545987 -0.000000 -0.167781 -0.000000
-0.084152 0.000000 )</i></div>
<div><i> freq ( 2) = 0.000000 [THz] =
0.000004 [cm-1]</i></div>
<div><i> ( 0.166188 0.000000 0.552429 0.000000
-0.023176 -0.000000 )</i></div>
<div><i> ( 0.166188 0.000000 0.552429 0.000000
-0.023176 -0.000000 )</i></div>
<div><i> ( 0.166188 0.000000 0.552429 0.000000
-0.023176 0.000000 )</i></div>
<div><i> freq ( 3) = 0.000000 [THz] =
0.000008 [cm-1]</i></div>
<div><i> ( 0.087255 0.000000 -0.002306 0.000000
0.570714 0.000000 )</i></div>
<div><i> ( 0.087255 0.000000 -0.002306 0.000000
0.570714 0.000000 )</i></div>
<div><i> ( 0.087255 0.000000 -0.002306 0.000000
0.570714 0.000000 )</i></div>
<div><i> freq ( 4) = 5.235913 [THz] =
174.651242 [cm-1]</i></div>
<div><i> ( 0.123126 0.000000 0.213241 0.000000
-0.000000 -0.000000 )</i></div>
<div><i> ( -0.342690 -0.000000 -0.593505 -0.000000
0.000000 0.000000 )</i></div>
<div><i> ( -0.342690 -0.000000 -0.593505 -0.000000
0.000000 0.000000 )</i></div>
<div><i> freq ( 5) = 7.799484 [THz] =
260.162777 [cm-1]</i></div>
<div><i> ( -0.000000 0.000000 0.000000 -0.000000
0.000000 0.000000 )</i></div>
<div><i> ( 0.707104 -0.000013 0.001900 -0.000000
-0.000000 -0.000000 )</i></div>
<div><i> ( -0.707104 0.000013 -0.001900 0.000000
-0.000000 0.000000 )</i></div>
<div><i> freq ( 6) = 7.799484 [THz] =
260.162777 [cm-1]</i></div>
<div><i> ( -0.000000 -0.000000 -0.000000 -0.000000
-0.000000 0.000000 )</i></div>
<div><i> ( 0.001900 0.000000 -0.707104 -0.000000
0.000000 -0.000000 )</i></div>
<div><i> ( -0.001900 -0.000000 0.707104 0.000000
0.000000 0.000000 )</i></div>
<div><i> freq ( 7) = 9.162102 [THz] =
305.614822 [cm-1]</i></div>
<div><i> ( -0.000000 0.000000 0.000000 0.000000
-0.246235 0.000000 )</i></div>
<div><i> ( 0.000000 -0.000000 -0.000000 0.000000
0.685335 -0.000000 )</i></div>
<div><i> ( 0.000000 0.000000 -0.000000 -0.000000
0.685335 0.000000 )</i></div>
<div><i> freq ( 8) = 9.170687 [THz] =
305.901189 [cm-1]</i></div>
<div><i> ( -0.213241 0.000000 0.123126 -0.000000
0.000000 -0.000000 )</i></div>
<div><i> ( 0.593505 -0.000000 -0.342690 0.000000
-0.000000 0.000000 )</i></div>
<div><i> ( 0.593505 -0.000000 -0.342690 0.000000
-0.000000 0.000000 )</i></div>
<div><i> freq ( 9) = 10.162710 [THz] =
338.991522 [cm-1]</i></div>
<div><i> ( 0.000000 0.000000 -0.000000 -0.000000
-0.000000 -0.000000 )</i></div>
<div><i> ( -0.000000 -0.000000 0.000000 0.000000
-0.707107 0.000000 )</i></div>
<div><i> ( -0.000000 -0.000000 -0.000000 0.000000
0.707107 0.000000 )</i></div>
<div><i> **************************************************************************</i></div>
</div>
<div><br>
</div>
<div>However, when I tried to compute phonon DOS in which a
mesh grid rather than a list of high symmetry kpoints was
declared, a different set of Gamma point phonon frequencies
appeared. The input file for DOS calculation is:</div>
<div><br>
</div>
<div>
<div><i> &input</i></div>
<div><i> asr='crystal'</i></div>
<div><i> amass(1)=178.49,</i></div>
<div><i> amass(2)=32.065,</i></div>
<div><i> ntyp=2</i></div>
<div><i> flfrc='HfS2.fc', flfrq='HfS2_DOS.freq'</i></div>
<div><i> dos=.true.</i></div>
<div><i> fldos='HfS2.dos'</i></div>
<div><i> deltaE=3</i></div>
<div><i> nk1=30, nk2=30, nk3=30,</i></div>
<div><i> /</i></div>
</div>
<div><br>
</div>
<div>The Gamma point frequencies are:</div>
<div><br>
</div>
<div>
<div> <i>diagonalizing the dynamical matrix ...</i></div>
<div><i><br>
</i></div>
<div><i> q = 0.0000 0.0000 0.0000</i></div>
<div><i> **************************************************************************</i></div>
<div><i> freq ( 1) = -0.000000 [THz] =
-0.000004 [cm-1]</i></div>
<div><i> ( 0.025759 -0.000000 -0.007450 -0.000000
-0.576727 -0.000000 )</i></div>
<div><i> ( 0.025759 -0.000000 -0.007450 -0.000000
-0.576727 -0.000000 )</i></div>
<div><i> ( 0.025759 -0.000000 -0.007450 -0.000000
-0.576727 0.000000 )</i></div>
<div><i> freq ( 2) = -0.000000 [THz] =
-0.000003 [cm-1]</i></div>
<div><i> ( -0.568506 0.000000 -0.097733 0.000000
-0.024130 -0.000000 )</i></div>
<div><i> ( -0.568506 0.000000 -0.097733 0.000000
-0.024130 -0.000000 )</i></div>
<div><i> ( -0.568506 0.000000 -0.097733 0.000000
-0.024130 0.000000 )</i></div>
<div><i> freq ( 3) = 0.000000 [THz] =
0.000005 [cm-1]</i></div>
<div><i> ( -0.097317 -0.000000 0.568969 -0.000000
-0.011697 -0.000000 )</i></div>
<div><i> ( -0.097317 -0.000000 0.568969 -0.000000
-0.011697 -0.000000 )</i></div>
<div><i> ( -0.097317 -0.000000 0.568969 -0.000000
-0.011697 0.000000 )</i></div>
<div><i> freq ( 4) = 5.235913 [THz] =
174.651242 [cm-1]</i></div>
<div><i> ( -0.000025 0.000000 0.246235 0.000000
-0.000000 -0.000000 )</i></div>
<div><i> ( 0.000070 -0.000000 -0.685335 -0.000000
0.000000 0.000000 )</i></div>
<div><i> ( 0.000070 -0.000000 -0.685335 -0.000000
0.000000 0.000000 )</i></div>
<div><i> freq ( 5) = 5.235913 [THz] =
174.651242 [cm-1]</i></div>
<div><i> ( 0.246234 0.000623 0.000025 0.000000
0.000000 -0.000000 )</i></div>
<div><i> ( -0.685333 -0.001733 -0.000070 -0.000000
-0.000000 -0.000000 )</i></div>
<div><i> ( -0.685333 -0.001733 -0.000070 -0.000000
0.000000 0.000000 )</i></div>
<div><i> freq ( 6) = 7.799484 [THz] =
260.162777 [cm-1]</i></div>
<div><i> ( 0.000000 -0.000000 0.000000 0.000000
0.000000 0.000000 )</i></div>
<div><i> ( 0.707105 -0.000010 0.001673 -0.000000
-0.000000 -0.000000 )</i></div>
<div><i> ( -0.707105 0.000010 -0.001673 0.000000
-0.000000 0.000000 )</i></div>
<div><i> freq ( 7) = 7.799484 [THz] =
260.162777 [cm-1]</i></div>
<div><i> ( 0.000000 -0.000000 -0.000000 -0.000000
-0.000000 0.000000 )</i></div>
<div><i> ( 0.001673 0.000000 -0.707105 -0.000000
0.000000 -0.000000 )</i></div>
<div><i> ( -0.001673 -0.000000 0.707105 0.000000
0.000000 0.000000 )</i></div>
<div><i> freq ( 8) = 9.672630 [THz] =
322.644206 [cm-1]</i></div>
<div><i> ( 0.000000 0.000000 -0.000000 0.000000
-0.246235 0.000000 )</i></div>
<div><i> ( 0.000000 -0.000000 0.000000 0.000000
0.685335 -0.000000 )</i></div>
<div><i> ( -0.000000 0.000000 0.000000 -0.000000
0.685335 0.000000 )</i></div>
<div><i> freq ( 9) = 10.162710 [THz] =
338.991522 [cm-1]</i></div>
<div><i> ( -0.000000 -0.000000 -0.000000 0.000000
-0.000000 -0.000000 )</i></div>
<div><i> ( -0.000000 -0.000000 0.000000 0.000000
-0.707107 0.000000 )</i></div>
<div><i> ( 0.000000 -0.000000 -0.000000 0.000000
0.707107 0.000000 )</i></div>
<div><i> **************************************************************************</i></div>
</div>
<div><br>
</div>
<div>I summarize the phonon frequencies for easier comparison:</div>
<div><b>Gamma-M-K-Gamma:</b> -0.0000 0.0000 0.0000
174.6512 260.1628 260.1628 305.6148 305.9012 338.9915</div>
<div><b>DOS: </b>-0.0000 -0.0000 0.0000 174.6512
174.6512 260.1628 260.1628 322.6442 338.9915</div>
<div><br>
</div>
<div>As can be seen, the phonon calculation along high
symmetry point shows a degenerate frequency at <b>
</b><span
style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><b>260.1628</b>
while the DOS calculation shows degeneracy at
<span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><b>174.6512
</b>and <span
style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><b>260.1628.</b> Moreover,
a new phonon mode with frequency
<span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><b>322.6442
</b>appears in the DOS calculation that is absent
from calculation along high symmetry directions.</span></span></span></span></div>
<div><span
style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><br>
</span></span></span></span></div>
<div>Why should the Gamma point frequency depend on the list
of kpoints one is diagonalizing dynamical matrices on? It
does not seem to be numerical error since the difference is
so huge. Can anyone help me understand it? Thank you very
much</div>
<div><span
style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><br>
</span></span></span></span></div>
<div><span
style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">FYI,
input file for ph.x is shown below:</span></span></span></span></div>
<div><span
style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><br>
</span></span></span></span></div>
<div><span
style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span
style="text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><i>
<div>phonons of HfS2</div>
<div> &inputph</div>
<div>prefix='Hf'</div>
<div>epsil=.true.</div>
<div>fildyn='HfS2.dyn',</div>
<div> outdir='./tmp/'</div>
<div>tr2_ph=1.0d-12</div>
<div> ldisp=.true</div>
<div> nq1=4</div>
<div> nq2=4</div>
<div> nq3=4</div>
<div> /</div>
</i></span></span></span></span></div>
-- <br>
<div class="gmail_signature">
<div dir="ltr">
<div>
<div style="font-size:12.8px">------------------------------------------------------------------------------------------------------------------------<br>
Jie Peng</div>
<div style="font-size:12.8px">PhD student<br>
2134 Glenn Martin Hall, Mechanical Engineering,
University of Maryland<br>
College Park, Maryland, USA<br>
Phone:(+1) 240-495-9445<br>
</div>
<div style="font-size:12.8px">Email: <a
href="mailto:jiepeng@umd.edu" target="_blank"
moz-do-not-send="true">jiepeng@umd.edu</a><br>
</div>
</div>
<div><br>
</div>
</div>
</div>
</div>
</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<br>
<pre wrap="">_______________________________________________
users mailing list
<a class="moz-txt-link-abbreviated" href="mailto:users@lists.quantum-espresso.org">users@lists.quantum-espresso.org</a>
<a class="moz-txt-link-freetext" href="https://lists.quantum-espresso.org/mailman/listinfo/users">https://lists.quantum-espresso.org/mailman/listinfo/users</a></pre>
</blockquote>
<br>
</body>
</html>