<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">jiepeng@umd.edu</a><br></div></div><div><br></div></div></div>
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