Dear Cyrille and Users<br><br> Thanks for your answer. However, I don't want to calculate the energy of vacuum; Really I want to draw the DOS and PDOS of the BULK graphite correctly. I don't know that I should use the +7.8 eV as the Fermi energy in the DOS diagram either set it to zero and rescale the other energies or something else ? <br>
<br><br><br><blockquote style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;" class="gmail_quote"> You should know that within DFT calculations the zero of energy of a periodic system is NOT the vacuum.<br>
</blockquote><br><br><br> where is the zero of energy here ? and in which way the QE chooses it ? <br> <br> <br> Also, can one compare this Fermi energy with the Fermi energy of another material, or is such comparison reliable ? <br>
<br><br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<br> If you want to get the energy of vacuum you can simulate for example a surface with the "supercell" method ie including empty space between slabs. You will get the vacuum energy (and therefore also the work function) by plotting the potential far away from you slabs in the "empty" region.<br>
<br>
cyrille<br>
<br>
Dear All<br>
<br>
I get positive Fermi energy (+7.8 eV) for bulk graphite by Quantum Espresso.<br>
Positive energy is meaningless for me here. Would you please say me that in<br>
whcih way QE selects the zero energy?<br>
As I know the vacuum should be considered as zero energy. I appreciate you<br>
in advance to solve the problem.<br>
<br>
--<br>
Sincerely Yours<br>
David G.<br>
JCU<br>
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