<div dir="ltr">Dear Wang,<br><br>In principle both the scf & nscf should give exactly the same value of Fermi energy if your calculations are converged w.r.t. the k-point sampling (since evaluation of Fermi energy involves numerical integration in k-space). The fact that that the two procedures give different energies suggest that the k-point mesh is not converged. Since these are numerical integrations, the more the no of k-points the more accurate is the value of the integral. Therefore for Guoying's case, the value of Fermi energy obtained from scf is more accurate than that from nscf as suggested by Hande.<br>
<br>If the difference in Fermi energy is quite large, what I would suggest is to increase the no. of k-points in the nscf cal. & redo it.<br><br>With regards,<br><br>Prasenjit.<br>
<br><div class="gmail_quote">2008/8/13 wangxinquan <span dir="ltr"><<a href="mailto:wangxinquan@tju.edu.cn" target="_blank">wangxinquan@tju.edu.cn</a>></span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div style="font-size: 10pt; font-family: verdana;">
<div align="left"><font face="Verdana" size="2">>>Dear Guoying</font></div>
<div align="left">>></div>
<div align="left">>> scf: k-mesh grids 10*10*10 (282kpoints in</div>
<div align="left">>> *.scf.out file)</div>
<div align="left">>> nscf: we give 121 kpoints along high symmetry direction</div>
<div align="left">>> </div>
<div align="left">>></div>
<div align="left">>>In order to find the Fermi energy, the code performs an integration in</div>
<div align="left">>>k-space and this integration is of course numerically performed over the</div>
<div align="left">>>kpoints you provide. In the nscf run, you provide a highly heterogeneous</div>
<div align="left">>>set of kpoints so the Fermi energy you get is not the same as the scf</div>
<div align="left">>>solution where the BZ is sampled more evenly (and also more densely in your</div>
<div align="left">>>case). As a result, you should trust the scf result.</div>
<div align="left"> </div>
<div align="left">Dear Guoying,</div>
<div align="left"> </div>
<div align="left"> In my opinion, you should use the nscf
results if you want to calculate the band</div>
<div align="left">structure. According to the example 08 of espresso-4.0.1,
the calculation </div>
<div align="left">of DOS for Ni follows three steps:1. pw.x
(scf);2.pw.x(nscf);3.dos.x(dos). The calculation </div>
<div align="left">of nscf modifies the wavefunctions obtained by scf
calculations. You will see</div>
<div align="left">that the k-points were identified manually in scf while
they were automatically selected in</div>
<div align="left">nscf. So the Fermi energy used in band structure
calculation should be the result from nscf.</div>
<div align="left"> I'm not sure that the
above suggestions are absolutely right. It's just my limited
experience.</div>
<div align="left"> You'd better investigate the README file in the
example 08 by yourself.</div>
<div align="left"> Hope this help.</div>
<div align="left"> </div>
<div align="left">Cheers,</div>
<div align="left">XQ Wang</div>
<div align="left"> </div>
<div align="left">
<div><font face="Verdana" size="2">
<p style="margin: 0cm 0cm 0pt;"><span lang="FR"><font size="3"><font face="Times New Roman">=====================================</font></font></span></p>
<p style="margin: 0cm 0cm 0pt;"><span lang="FR"><font size="3"><font face="Times New Roman">X.Q. Wang </font></font></span></p>
<p style="margin: 0cm 0cm 0pt;"><span lang="FR"><a href="mailto:wangxinquan@tju.edu.cn" target="_blank"><font face="Times New Roman" size="3">wangxinquan@tju.edu.cn</font></a></span></p>
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<p style="margin: 0cm 0cm 0pt;"><font size="3"><font face="Times New Roman"><span lang="EN-US">Tianjin</span><span lang="EN-US">
University</span></font></font></p>
<p style="margin: 0cm 0cm 0pt;"><span lang="EN-US"><font face="Times New Roman" size="3">92 Weijin Road, Tianjin, P. R.
China</font></span></p>
<p style="margin: 0cm 0cm 0pt;"><span lang="EN-US"><font face="Times New Roman" size="3">tel:86-22-27890268, fax:
86-22-27892301</font></span></p>
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