[Pw_forum] Fermi energy in 'scf' and 'nscf'(XQ Wang)

wangxinquan wangxinquan at tju.edu.cn
Wed Aug 13 10:26:57 CEST 2008

>>Dear Guoying
>>             scf:           k-mesh grids   10*10*10  (282kpoints in
>> *.scf.out file)
>>           nscf:           we give 121 kpoints along high symmetry direction
>>In order to find the Fermi energy, the code performs an integration in
>>k-space and this integration is of course numerically performed over the
>>kpoints you provide. In the nscf run, you provide a highly heterogeneous
>>set of kpoints so the Fermi energy you get is not the same as the scf
>>solution where the BZ is sampled more evenly (and also more densely in your
>>case). As a result, you should trust the scf result.

Dear Guoying,

    In my opinion, you should use the nscf results if you want to calculate the band
structure. According to the example 08 of espresso-4.0.1, the calculation 
of DOS for Ni follows three steps:1. pw.x (scf);2.pw.x(nscf);3.dos.x(dos). The calculation 
of nscf modifies the wavefunctions obtained by scf calculations. You will see
that the k-points were identified manually in scf while they were automatically selected in
nscf. So the Fermi energy used in band structure calculation should be the result from nscf.
    I'm not sure that the above suggestions are absolutely right. It's just my limited experience.
 You'd better investigate the README file in the example 08 by yourself.
    Hope this help.

XQ Wang

X.Q. Wang 
wangxinquan at tju.edu.cn
School of Chemical Engineering and Technology
Tianjin University
92 Weijin Road, Tianjin, P. R. China
tel:86-22-27890268, fax: 86-22-27892301
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