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<div>Dear nicola,</div><div> Thank you so much for your explanation.</div><div> I made a further investigate.</div><div> I tried to calculate a series of diamond phonon dispersion respect to different ecutrho. </div><div> They are all calculated under the following condition</div><div> 1. scf condition: kmesh=4,4,4 ecut=27, pseudopotential=C.pz-rrkjus.UPF, conv_thr = 1.0d-10</div><div> 2. phonon condition: qmesh=4,4,4 tr2_ph=1.d-14</div><div> <br> I plot these phonon dispersion together (here is the image <a href="https://pasteboard.co/GDDpray.png" _src="https://pasteboard.co/GDDpray.png">https://pasteboard.co/GDEmkd3.png</a> ) . We can see that except for ecutrho=75, dispersion for all other cases are quite close. The biggest deviation for ecutrho=100 to 450 is 8.2275cm^-1, while for ecutrho=150 to 450, the biggest deviation is almost as negligible as 0.7cm^-1. This is quite surprising，because the tutorial link recommended high ecutrho=450 for converged calculation.</div><div><br></div><div> Besides, I extract X point frequency from the above dispersions and plot them with respect to ecutrho ( here is the image <a href="https://pasteboard.co/GDEqdDb.png" _src="https://pasteboard.co/GDEqdDb.png" style="line-height: 1.5;">https://pasteboard.co/GDEqdDb.png</a> )</div><div> On the other hand, I <span style="line-height: 1.5;">can also calculate phonon frequency at X point (0,1,0) using ph.x directly with the same scf parameter as the above. Again plot them with respect to ecutrho</span><span style="line-height: 1.5;"> (Here is the image </span><a href="https://pasteboard.co/GDDu3wt.png" _src="https://pasteboard.co/GDDu3wt.png" style="line-height: 1.5;">https://pasteboard.co/GDDu3wt.png</a> <span style="line-height: 1.5;">). </span></div><div> From these two plots, I got confused. The convergence behaviour of matdyn.x and ph.x at the same point is not the same. The convergence of dispersion is much quicker ( above ecutrho=200) then convergence of single point ph.x calc ( above ecutrho=400 ). Is it generally true?</div><div><br></div><div>best regards</div>
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