<div dir="ltr">Dear QE users and developers,<div><br></div><div>Recently, I was trapped by a question about the critical temperature Tc for a very long time.<br>In one calculation, I can successfully get the lamda (electron-phonon coupling) and Tc like:</div><div>lambda        omega_log          T_c<br>   0.15006       335.625              0.000<br>   0.23881       279.676              0.007<br>   0.37627       249.217              0.724<br>   0.55241       226.383              3.971<br>   0.74555       208.449              8.401<br>   0.93962       193.607             12.205<br>   1.12670       180.939             14.944</div><div>   ...                 ...                       ....<br>  </div><div>But when I add two flags: <br>el_ph_sigma=0.005,<br>el_ph_nsigma=10,</div><div><br>into the system. <a href="http://elph.in">elph.in</a> file. I obtained the result:<br>lambda        omega_log          T_c<br>   0.05937      1332.783          *********<br>   0.06470      1324.945          *********<br>   0.06835      1309.450          *********</div><div>   ...                 ...                       ....  <br><br><p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;text-align:justify;line-height:125%;font-size:10.5pt;font-family:Calibri,sans-serif"><span lang="EN-US">I compare the phonon dispersion, both are
identical and without imaginary frequency. I also check</span></p><p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;text-align:justify;line-height:125%;font-size:10.5pt;font-family:Calibri,sans-serif"><span lang="EN-US">the elph.inp_lambda.*
file, no imaginary frequency also. </span><span style="font-size:10.5pt">I use the pwscf 6.3 version.</span></p><p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;text-align:justify;line-height:125%;font-size:10.5pt;font-family:Calibri,sans-serif"><span style="font-size:10.5pt"><br></span></p><p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;text-align:justify;line-height:125%;font-size:10.5pt;font-family:Calibri,sans-serif"><span style="font-size:10.5pt">Both calculations are identical except for these two parameters (without/with).<b> Lamda changes significantly.</b></span></p><p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;text-align:justify;line-height:125%;font-size:10.5pt;font-family:Calibri,sans-serif"><b><span lang="EN-US">I am wondering how much effect of these
two flags in pwscf on the superconductivity?</span></b><span lang="EN-US"> I
checked the manual, </span></p><p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;text-align:justify;line-height:125%;font-size:10.5pt;font-family:Calibri,sans-serif"><span lang="EN-US">but the related info is limited. In the latest version of 6.4, the official website has deleted these two flags.</span></p><p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;text-align:justify;line-height:125%;font-size:10.5pt;font-family:Calibri,sans-serif">

</p><p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;text-align:justify;line-height:125%;font-size:10.5pt;font-family:Calibri,sans-serif"><span lang="EN-US">Why these two parameters would lead to the
infinite Tc?  </span></p><p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;text-align:justify;line-height:125%;font-size:10.5pt;font-family:Calibri,sans-serif"><span lang="EN-US">Thanks a lot!</span></p><p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;text-align:justify;line-height:125%;font-size:10.5pt;font-family:Calibri,sans-serif"><span lang="EN-US"><br></span></p><p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;text-align:justify;line-height:125%;font-size:10.5pt;font-family:Calibri,sans-serif">Best wishes,</p><p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;text-align:justify;line-height:125%;font-size:10.5pt;font-family:Calibri,sans-serif">Zhibin</p><p class="MsoNormal" style="margin:0cm 0cm 0.0001pt;text-align:justify;line-height:125%;font-size:10.5pt;font-family:Calibri,sans-serif">Tongji University</p></div></div>