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<DIV><FONT face=Verdana size=2>>Dear Wang,</FONT></DIV>
<DIV><FONT face=Verdana size=2> Dear Prasenjit,</DIV>
<DIV>
<DIV>></DIV>
<DIV>>In principle both the scf & nscf should give exactly the same value of Fermi</DIV>
<DIV>>energy if your calculations are converged w.r.t. the k-point sampling</DIV>
<DIV>>(since evaluation of Fermi energy involves numerical integration in</DIV>
<DIV>>k-space).The fact that that the two procedures give different energies</DIV>
<DIV>>suggest that the k-point mesh is not converged. Since these are numerical</DIV>
<DIV>>integrations, the more the no of k-points the more accurate is the value of</DIV>
<DIV>>the integral. Therefore for Guoying's case, the value of Fermi energy</DIV>
<DIV>>obtained from scf is more accurate than that from nscf as suggested by</DIV>
<DIV>>Hande.</DIV>
<DIV>></DIV>
<DIV>>If the difference in Fermi energy is quite large, what I would suggest is to</DIV>
<DIV>>increase the no. of k-points in the nscf cal. & redo it.</DIV>
<DIV>
<DIV> </DIV>
<DIV>As I'm a newbie in this field, the basic concept of quantum mechanics and
</DIV>
<DIV>condensed matter physics(DFT, the Bloch theory and plane wave) are
rather</DIV>
<DIV>abstract for me, following contents may have some
misunderstanding of your suggestions.<IMG src="cid:__0@Foxmail.net"> </DIV>
<DIV> </DIV>
<DIV>From scf and nscf results, fermi energies should be consistent
with each other if they were </DIV>
<DIV>evaluated (integrated and converged) with respect to the same
k-points. nscf (non-scf) only </DIV>
<DIV>involves integrations of the special k-points using
the charge density results from scf (which</DIV>
<DIV>have been saved in the /tmp folder). No iteration is involved in
nscf. </DIV>
<DIV> </DIV>
<DIV>Furthermore nscf obtains the mean
value of the integration of wavefunctions when
the k-points </DIV>
<DIV>were sampled by Monkhorst-Pack method. Sometimes k-points are not
so dense to integrate </DIV>
<DIV>accurately (certain key points may be ignored). Compare with
nscf, the fermi energy in scf </DIV>
<DIV>should be mostly reasonable.</DIV>
<DIV> </DIV>
<DIV>When we want to calculation DOS we need to add more k-points for
nscf and confirm that the </DIV>
<DIV>identical fermi energies can be achieved. Otherwise we
should trust the fermi energy from scf results</DIV>
<DIV>when we deal with band structures and dos. </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>Best regards,</DIV>
<DIV>XQ Wang</DIV>
<DIV>
<DIV>
<DIV><FONT face=Verdana size=2>
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