<div>Thank you for your reply.</div>
<div>Recently I have read a paper published in Nano letters titled "Tuning the Graphene work function by electric field effect"(<a href="http://pubs.acs.org/doi/pdf/10.1021/nl901572a">http://pubs.acs.org/doi/pdf/10.1021/nl901572a</a>). The main conclusion is that the work function of graphene can be adjusted as the gate voltage tunes the Fermi level across the charge neutrality point. The tunable work function makes graphene an attractive material for low contact barrier electrodes. Motivated by this attractive application, I tried to calculate the work function under external electric field.</div>
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<div>Before the calculation, I firstly tried to understand the definition of the work function and how it is calculated in Pwscf package. The literature (J. Phys.: condens. Matter 11(1999) 2689-2696) mentioned in the description of the workFct_example directory shows the macroscopic-average method to the calculation of work functions. The work function is the minimum energy required to extract one electron to an infinite distance form the surface and its value is equivalent to the mean electrostatic potential energy across the metal surface minus the Fermi energy. And thus the question whether electric field can reflect the Fermi level of a certain material surface arises.</div>
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<div>The example31 shows how to perform electronic structure calculations using pwscf package for a system undergoing the presence of a static homogeneous finite electric field. As a test, I firstly calculated the work function of graphene at zero external electric field and the calculated value is consistent with the previous published paper(PRL_94_236602) and the experimental result. Secondly, I calculated the work function at finit external electric field, and then I use the pp.x and average.x to get the work function as at the zero external efield. It seems that the calculated work function value is different from that under zero external efield. But I don't know whether the calculated work function value is reasonable.</div>
<div> </div>
<div>My questions are as follows:</div>
<div>1) Whether the work function would be changed under a finite external efield?</div>
<div>2) Can I use the method calculating work function under zero efield to calculate work function under finite efield?</div>
<div>3) Can the plot number 11 in pp.x package deal with the potential under finite efield?</div>
<div> </div>
<div>Any suggestion or comment is appreciated. Thank you in advance. </div>
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<div>sincerely,</div>
<div> </div>
<div><br><br> </div>
<div class="gmail_quote">2009/9/16 Stefano Baroni <span dir="ltr"><<a href="mailto:baroni@sissa.it">baroni@sissa.it</a>></span><br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">
<div style="WORD-WRAP: break-word">Hi. before calculating anything, I think it is important to define and understand what one is going to calculate. Would you please give us a definition of "work function under an external field" and compare/contrast it to the accepted definition of "workfunction at zero field"? Thanks - SB
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<div>On Sep 16, 2009, at 3:53 AM, 程迎春 wrote:</div><br></div></div>
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<div>Dear pwscf users,</div>
<div> The PWscf can calculate the workfunction in slab model and the electronic structure under external efield. I am concerning that whether it it correct to calculate the workfunction of a certain materials under external efield? Thank you in advance.<br clear="all">
</div>
<div></div><br>-- <br>Y. C. Cheng<br>Department of Physics<br>Nanjing University<br>Nanjing 210093<br>P. R. China<br>Tel: 86-25-83592907<br>Email: <a href="mailto:yccheng.nju@gmail.com" target="_blank">yccheng.nju@gmail.com</a><br>
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<div style="MARGIN: 0px"><font size="3"><span style="FONT-SIZE: 12px">---</span></font></div>
<div style="MARGIN: 0px"><font size="3"><span style="FONT-SIZE: 12px">Stefano Baroni - SISSA</span></font><font size="3"><span style="FONT-SIZE: 12px"> </span></font><font size="3"><span style="FONT-SIZE: 12px">&</span></font><font size="3"><span style="FONT-SIZE: 12px"> </span></font><font size="3"><span style="FONT-SIZE: 12px">DEMOCRITOS National Simulation Center - Trieste</span></font></div>
<div style="MARGIN: 0px"><font size="3"><span style="FONT-SIZE: 12px"><a href="http://stefano.baroni.me/" target="_blank">http://stefano.baroni.me</a> [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)</span></font></div>
<div style="FONT-SIZE: 12px; MIN-HEIGHT: 14px; MARGIN: 0px"><br style="FONT-SIZE: 12px"></div>
<div style="FONT-SIZE: 12px; MIN-HEIGHT: 14px; MARGIN: 0px"><span style="FONT-SIZE: 14px">
<div style="MARGIN: 0px"><font size="3"><span style="FONT-SIZE: 12px">La morale est une logique de l'action comme la logique est une morale de la pensée - Jean Piaget</span></font></div>
<div style="MARGIN: 0px"><font size="3"><span style="FONT-SIZE: 12px"><br></span></font></div></span></div>
<div style="MARGIN: 0px"><font size="3"><span style="FONT-SIZE: 12px">Please, if possible, don't</span></font><font size="3"><span style="FONT-SIZE: 12px"> </span></font><font size="3"><span style="FONT-SIZE: 12px">send me MS Word or PowerPoint attachments</span></font></div>
<div style="MARGIN: 0px"><font size="3"><span style="FONT-SIZE: 12px">Why? See:</span></font><font size="3"><span style="FONT-SIZE: 12px"> </span></font><font color="#0023e9" size="3"><span style="FONT-SIZE: 12px"><a href="http://www.gnu.org/philosophy/no-word-attachments.html" target="_blank">http://www.gnu.org/philosophy/no-word-attachments.html</a></span></font></div>
<div><font color="#0023e9" size="3"><span style="FONT-SIZE: 12px"><br></span></font></div></div></div></span><br></div></span><br></div></span><br></div></span><br></div></span><br></div><br></div></div><br>_______________________________________________<br>
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<div></div><br>-- <br>Y. C. Cheng<br>Department of Physics<br>Nanjing University<br>Nanjing 210093<br>P. R. China<br>Tel: 86-25-83592907<br>Email: <a href="mailto:yccheng.nju@gmail.com">yccheng.nju@gmail.com</a><br>