<div dir="ltr"><div>Dear Shubham,</div><div>I will add a little contribution to the discussion. Prior to it, I would strongly recommend, as it has been correctly pointed out, that before doing ANY calculation</div><div>you become aware (using tutorials, textbooks and so on) about exactly what you are calculating, what are the units, and so on. In many cases (but I do not know if</div><div>this is your case!), skipping a necessary initial (self!) training produces much more waste of time than spending time in understanding how things work.</div><div><br></div><div>After inspection of the plots you sent, it seems that the problem you have is other than a magnitude mismatch. Indeed, a magnitude mismatch is just</div><div>a scaling factor, all the bands get multiplied by 10 or 100 or any odd factor that might be obtained by combinations of Ry = 13.6 eV, bohr radius and any</div><div>other relevant scale unit might apply in this case.</div><div><br></div><div>What I simply tried is to superimpose the two phonon band structures and to stretch one to try to make it overlap with the other. No success in doing that.</div><div>Effectively, you could for example look at the 6th band. The one on the left is almost flat, the one on the right is not. Moreover, in the left plot its maximum is</div><div>maybe the small dip at the x-axis center, whereas on the right there are two pronounced maxima around the x-axis extrema. As further proof, the 7-th band</div><div>shares a frequency range with the 6th one on the right, whereas in the left the two are separated by a small gap.</div><div>So, I would conclude that the two band structures do not differ by a scaling factor and are, for some reason, definitely different! This is also confirmed by the s</div><div>econd image you sent, with three plots. In that case, the right plot was obtained after multiplying the middle one by a factor and indeed the two band structures </div><div>look identical, apart from the y-axis scale.</div><div><br></div><div>How could it happen? Some possible answers:</div><div>i) you diagonalized a wrong matrix (for example: did you properly include the mass factors?)</div><div>ii) you are not plotting the same quantity. If I'm not wrong, and there is not just a scaling factor between left and right, could it be that for example</div><div>when you make the diagonalization you get the squares of the frequencies, which would explain the NOT UNIFORM stretching of one band structure with respect to</div><div>the other? This or similar things can explain your issue if you diagonalized the matrix by hand, not of course if the diagonalization was produced</div><div>by a quantum-espresso executable, where units are correctly fixed.</div><div><br></div><div>So, the suggestion is to start from scratch, trying to understand, at each step, what you're doing, which quantity you obtained and with which units. I'm pretty sure that</div><div>it will not be that difficult for you to figure out what's happening!</div><div><br></div><div>Giovanni</div><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><span style="color:rgb(0,0,0)">-- <br><br>Giovanni Cantele, PhD<br>CNR-SPIN<br>c/o Dipartimento di Fisica<br>Universita' di Napoli "Federico II"<br>Complesso Universitario M. S. Angelo - Ed. 6<br>Via Cintia, I-80126, Napoli, Italy<br><a href="mailto:giovanni.cantele@spin.cnr.it" style="color:rgb(17,85,204)" target="_blank">e-mail: giovanni.cantele@spin.cnr.it</a><br>Phone: +39 081 676910<br>Skype contact: giocan74<br><br>ResearcherID: <a href="http://www.researcherid.com/rid/A-1951-2009" style="color:rgb(17,85,204)" target="_blank">http://www.researcherid.com/rid/A-1951-2009</a><br>Web page: </span><a href="https://sites.google.com/view/giovanni-cantele/home" style="color:rgb(17,85,204)" target="_blank">https://sites.google.com/view/giovanni-cantele/home</a><br></div></div></div><br></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">Il giorno mar 8 apr 2025 alle ore 17:03 Shubham Patel <<a href="mailto:spatelphy@iitkgp.ac.in">spatelphy@iitkgp.ac.in</a>> ha scritto:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Dear developers and users,<br>
<br>
I am trying to calculate the frequencies (freqs) using Quantum Espresso PHonon calculations as well as using dynamical matrices generated using matdyn.x. I find that there is a unit mismatch in the freqs which gives rise to a magnitude difference. In the first case, I calculate phonon band structure using matdyn.x --> plotband.x. While in the second case I generate dynamical matrices using matdyn.x and then diagonalize the matrices along the kpath and generated exactly same band dispersion except the magnitude on the y-axis (frequency range). Could anyone please tell what is this factor which brings the magnitude mismatch? I am also attaching a figure to compare.<br>
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Thank you very much for any help.<br>
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Sincerely,<br>
Shubham_______________________________________________________________________________<br>
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