<div dir="ltr"><div dir="auto"><div>Hi,</div><div><br></div><div>It is normal, the Fermi energy shows the energy of highest occupied electron and it does not necessary is exactly on zero.</div><div><br></div><div>You can shift All energies by an additive constant without no problem. For one single system it is ok to shift the energies by an additive constant. (Like add +2.0508 to move the Fermi level to zero) and it is not changing the physics of the result, just the way you are presenting.</div>
<div><br></div><div>However, BE CAREFUL! It dos not mean that you can align two different systems using this method. <br></div><div><br></div><div style>From the QE website:</div><div><br></div><div><em style="color:rgb(77,77,77);font-family:Arial,Helvetica,sans-serif;font-size:14px;line-height:20px;margin:0px;padding:0px"><br>
</em></div><div><em style="color:rgb(77,77,77);font-family:Arial,Helvetica,sans-serif;font-size:14px;line-height:20px;margin:0px;padding:0px">“The value of the Fermi energy (as well as of any energy, for that matter) depends upon the reference level. What you are referring to is probably the “Fermi energy referred to the vacuum level” (i.e. the work function). In order to obtain that, you need to know what the vacuum level is, which cannot be said from a bulk calculation only”></em><span style="color:rgb(77,77,77);font-family:Arial,Helvetica,sans-serif;font-size:14px;line-height:20px"> </span><span style="color:rgb(77,77,77);font-family:Arial,Helvetica,sans-serif;font-size:14px;line-height:20px">(Stefano Baroni, Sept. 2008).</span><br>
</div><div><br></div><div><a href="http://www.quantum-espresso.org/?page_id=364">http://www.quantum-espresso.org/?page_id=364</a><br></div><div><br></div><div><br></div><div>Best regards,</div><div><br></div><div style>Filipe Lima - PhD Student - University of São Paulo, Brazil.</div>
<div><br></div><div><br>On 04/04/2013, at 22:30, Shamsu Abubakar <<a href="mailto:say457@yahoo.co.uk" target="_blank">say457@yahoo.co.uk</a>> wrote:<br><br></div><blockquote type="cite"><div><div style="font-size:14pt;font-family:'times new roman','new york',times,serif">
Thank you Mr. Robert for your kind response.<br>I will include the verbosity='high' and repeat the calculations. However, you made mention that, when i plotted the DOS there is need to shift my Fermi level to zero; that i did not understand very well. My question is, How to shift my Fermi to zero?. Secondly, I always see my Fermi energy at the end of my scf calculation.'' the Fermi energy is -2.0508'', before total energy line. Does it mean -2.0508 is my actual Fermi energy? because the zero point in the DOS graph is just a reference point. Lastly, for my plotting software, i used Qtiplot. Usually, after <span><span style="font-size:14pt">my ./dos.x input and output, i take my 'dos' directly to plot my DOS. Therefore, I don't know if you or someone can help with some guide about
it.<br><br>Once again thank you and Best regards.<br></span></span><br><div><div><span><span style="font-size:14pt">Shamsu Abubakar</span></span><span style="font-size:14pt"></span></div></div><div><div><span><span style="font-size:14pt">Postgraduate student</span></span><span style="font-size:14pt"></span></div>
</div><div><div><span><span style="font-size:14pt">Department of Physics</span></span><span style="font-size:14pt"></span></div></div><div style="background-color:white"><span><span style="font-size:14pt">University Putra Malaysia</span></span><span style="font-size:14pt"></span></div>
<div><span><br></span></div><div><br></div> <div style="font-family:'times new roman','new york',times,serif;font-size:14pt"> <div style="font-family:'times new roman','new york',times,serif;font-size:12pt">
<div dir="ltr"> <font face="Arial"> <hr size="1"> <b><span style="font-weight:bold">From:</span></b> Robert Hembree <<a href="mailto:hembreerofphysics@gmail.com" target="_blank">hembreerofphysics@gmail.com</a>><br>
<b><span style="font-weight:bold">To:</span></b> 'Shamsu Abubakar' <<a href="mailto:say457@yahoo.co.uk" target="_blank">say457@yahoo.co.uk</a>>; 'PWSCF Forum' <<a href="mailto:pw_forum@pwscf.org" target="_blank">pw_forum@pwscf.org</a>> <br>
<b><span style="font-weight:bold">Sent:</span></b> Friday, 5 April 2013, 1:17<br> <b><span style="font-weight:bold">Subject:</span></b> RE: [Pw_forum] Fermi energy reference point shift from 0 to -2<br> </font> </div> <br>
<div><div><div><div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Dear Shamsu</span></div><div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span></div>
<div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Your input file and parameters are fine. When you plot the DOS you need to shift your Fermi level to zero if you want the gap to show up at zero. </span></div>
<div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Add the line</span></div><div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">verbosity = ‘high’ </span></div>
<div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">to the control part of your input file and run pw.x again. Then you can grep your output file</span></div><div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">less scf.out | grep ‘Fermi energy’</span></div>
<div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span></div><div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">You should get a line that looks like this:</span></div>
<div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">the Fermi energy is -1.6709 ev</span></div><div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span></div>
<div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">When you plot your DOS, for instance in gnuplot you would now plot</span></div><div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span></div>
<div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">plot ‘Graph01.dos’ ($1-(-1.6709)):2 w l</span></div><div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">and you should see your plot with the bandgap and dispersion at zero. </span></div>
<div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span></div><div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">When you do these calculations the Fermi level will rarely show up at exactly zero.</span></div>
<div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span></div><div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Robert</span></div><div><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"> </span></div>
<div><div style="border-style:solid none none;border-top-color:rgb(181,196,223);border-top-width:1pt;padding:3pt 0in 0in"><div><b><span style="font-size:10pt;font-family:Tahoma,sans-serif">From:</span></b><span style="font-size:10pt;font-family:Tahoma,sans-serif"> <a href="mailto:pw_forum-bounces@pwscf.org" target="_blank">pw_forum-bounces@pwscf.org</a> [<a href="mailto:pw_forum-bounces@pwscf.org" target="_blank">mailto:pw_forum-bounces@pwscf.org</a>] <b>On Behalf Of </b>Shamsu Abubakar<br>
<b>Sent:</b> Wednesday, April 03, 2013 8:23 PM<br><b>To:</b> <a href="mailto:pw_forum@pwscf.org" target="_blank">pw_forum@pwscf.org</a><br><b>Subject:</b> [Pw_forum] Fermi energy reference point shift from 0 to -2</span></div>
</div></div><div> </div><div><div><div><div><div><div style="background-color:white"><span style="font-size:14pt">Dear <span>Q.E Users.</span></span></div></div><div><div><span><span style="font-size:14pt">I have a system of 4x4 graphene supercell, comprising 32 carbon atoms. I sucessfully run all the calculations i.e scf,nscf and other postprocessing such as DOS and PDOS. But the main problem i'm facing currently is on the density of state. Usually, i consider zero to be my fermi reference energy point in my ./dos.x input file, forexample,from -10 and 10 as my Emin and Emax respectivily. For pristine graphene,i expect to always see the dispersion at the zero vicinity, showing a semi metallic behavior, but surprisingly, its always moving away from zero to around -2, in the valence band side which i knew is unsual for pristine graphene. However, when i combine graphene with GaAs nanostructure, most of the interesting properties interms of orbitals contributions (PDOS), also resides on similar point -2. That is some of the contributions that are
supposed to be seen at the vicinity of the fermi level, now moved to another point -2. Also, i consider changing the smearing from marzari-vanderbilt to Fermi- Dirac, but similar properties were observed. I decided to consider only 1x1, and 2x2 graphene supercell alone, still similar properties i observed also. In fact, i even consider changing my pseudopotential from pw91 to pbe.rrkjus still no progress. My problem now, i don't know what really causes these shift from 0 to -2. </span></span><span style="font-size:14pt"></span></div>
</div><div><div><span><span style="font-size:14pt">I attached one of my graphene scf input file for your verification and advice.</span></span><span style="font-size:14pt"></span></div></div><div><div><span style="font-size:14pt"> </span></div>
</div><div><div><span><span style="font-size:14pt"> &CONTROL</span></span><span style="font-size:14pt"><br><span> title = 'Graphene monolayer01',</span><br><span> prefix = 'Graph01',</span><br>
<span> calculation = 'scf' ,</span><br><span> restart_mode = 'from_scratch' ,</span><br><span> outdir = '/home//???/espresso-4.1.2/bin/' ,</span><br>
<span> pseudo_dir = '/home//???/???/espresso-4.1.2/upf_files/' ,</span><br><span> </span><br><span> tstress = .true. ,</span><br><span> tprnfor = .true. ,</span><br>
<span> /</span><br><span> &SYSTEM</span><br><span> ibrav = 4,</span><br><span> celldm(1) = 18.59490373,</span><br><span> celldm(3) = 1.80,</span><br><span> nat = 32,</span><br>
<span> ntyp =
1,</span><br><span> ecutwfc = 34.D0 ,</span><br><span> tot_charge = 0.000000,</span><br><span> occupations = 'smearing' ,</span><br><span> degauss = 0.02 ,</span><br>
<span> smearing = 'fermi-dirac' ,</span><br><span> </span><br><span> /</span><br><span> &ELECTRONS</span><br><span> conv_thr = 1.D-8 ,</span><br><span> mixing_beta = 0.7D0 ,</span><br>
<span> /</span><br><span>ATOMIC_SPECIES</span><br><span> C 12.00000 C.pw91-van_ak.UPF </span><br><span> </span><br><span>ATOMIC_POSITIONS (angstrom)</span><br><span>C 1.229999657 0.709326753 1.999999753</span><br>
<span>C 2.459999165 1.419486000 1.999999874</span><br><span>C 3.689999208 0.709327391 1.999999822</span><br><span>C 4.920000000 1.419486496 1.999999944</span><br><span>C 4.920000000 2.839880146 2.000000125</span><br>
<span>C <a href="tel:6.149999990" value="+16149999990" target="_blank">6.149999990</a> 3.549976521 1.999999907</span><br><span>C 3.690000010
3.549976521 1.999999907</span><br><span>C 2.459999764 2.839879152 2.000000067</span><br><span>C 6.150000792 0.709327391 1.999999822</span><br><span>C 7.380000835 1.419486000 1.999999874</span><br>
<span>C 7.380000236 2.839879152 2.000000067</span><br><span>C 8.610000005 3.549975943 1.999999891</span><br><span>C <a href="tel:8.609999654" value="+18609999654" target="_blank">8.609999654</a> 4.970023341 2.000000208</span><br>
<span>C 9.840000000 5.680120078 2.000000200</span><br><span>C 7.379999382 5.680120770 2.000000152</span><br><span>C <a href="tel:6.149999800" value="+16149999800" target="_blank">6.149999800</a> 4.970024086 2.000000150</span><br>
<span>C 4.920000000 5.680121474 2.000000132</span><br><span>C 3.690000200 4.970024086 2.000000150</span><br><span>C 8.610000343 0.709326753 1.999999753</span><br><span>C 9.840000000
1.419485253 1.999999874</span><br><span>C 9.840000000 2.839878353 2.000000070</span><br><span>C 11.069999995 3.549975943 1.999999891</span><br><span>C 11.070000346 4.970023341 2.000000208</span><br>
<span>C 12.300000618 5.680120770 2.000000152</span><br><span>C 12.300001137 7.100514050 2.000000166</span><br><span>C 13.530000464 7.810673002 1.999999744</span><br><span>C
11.070000830 7.810672948 1.999999928</span><br><span>C 9.840000000 7.100514025 2.000000287</span><br><span>C <a href="tel:8.609999170" value="+18609999170" target="_blank">8.609999170</a> 7.810672948 1.999999928</span><br>
<span>C 7.379998863 7.100514050 2.000000166</span><br><span>C <a href="tel:6.149999536" value="+16149999536" target="_blank">6.149999536</a> 7.810673002 1.999999744</span><br><span>C 4.920000000 7.100514261 2.000000041</span><br>
<span> </span><br><span>K_POINTS automatic </span><br><span>
6 6 1 0 0 0 </span></span></div></div><div><div><span style="font-size:14pt"> </span></div></div><div><div><span><span style="font-size:14pt">Thank you for your kind response.</span></span><span style="font-size:14pt"></span></div>
</div><div><div><span style="font-size:14pt"> </span></div></div><div><div><span><span style="font-size:14pt">Shamsu Abubakar</span></span><span style="font-size:14pt"></span></div></div><div><div><span><span style="font-size:14pt">Postgraduate student</span></span><span style="font-size:14pt"></span></div>
</div><div><div><span><span style="font-size:14pt">Department of Physics</span></span><span style="font-size:14pt"></span></div></div><div style="background-color:white"><span><span style="font-size:14pt">University Putra Malaysia</span></span><span style="font-size:14pt"></span></div>
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