<div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Hi Mehrdad,</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">I forgot that you could just set ibrav = 3 instead of using the conventional BCC unit cell. That way you can just use one atom in the calculation. Also, don't forget to set a non-zero starting magnetization and change ecutrho to be 1080. If you make these 3 adjustments to your previous input file for the bulk BCC Fe it should work.<br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">I did a quick calculation of bulk BCC Fe on my laptop and got 329.27274577 Ry. Using your supercell energies I got a vacancy formation energy of 1.69 eV. Pretty close to the 1.66 eV reported by Jiang et al. that your reference uses. They used PW91-GGA, different PAW datasets and different software so I think that's pretty good. Double-check for yourself though, of course.</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Best,<br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br clear="all"></div><div><div dir="ltr" class="m_-7280164835633312346gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div><div><span style="font-family:arial,helvetica,sans-serif"><font size="2"><span style="color:rgb(102,102,102)"><b><span class="gmail_default" style="font-family:arial,helvetica,sans-serif">
</span></b></span></font></span><div style="font-family:arial,helvetica,sans-serif">Kevin May, PhD<br></div><div style="font-family:arial,helvetica,sans-serif">Postdoctoral Associate</div><div style="font-family:arial,helvetica,sans-serif">Department of Materials Science and Engineering</div><div style="font-family:arial,helvetica,sans-serif">Massachusetts Institute of Technology</div>
</div></div></div></div></div></div></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Jun 18, 2019 at 10:30 PM Kevin May <<a href="mailto:kmay@mit.edu" target="_blank">kmay@mit.edu</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Hi Mehrdad,</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">So you are indeed using an isolated Fe atom as your reference state. That is not the conventional chemical potential for elemental iron. To have a fair comparison to the calculated value the literature, please try a vc-relax calculation of ferromagnetic BCC iron (like this CIF file: <a href="https://www.crystallography.net/cod/9008536.cif" target="_blank">https://www.crystallography.net/cod/9008536.cif</a>). Divide the energy by 2 (since there are two atoms per unit cell) to get the chemical potential reference for iron. See my comment from the last email:</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div style="font-family:arial,helvetica,sans-serif"><span class="gmail_default" style="font-family:arial,helvetica,sans-serif"></span>By<b>
E(single Fe) you mean 1/2 the energy of ferromagnetic BCC Fe (2 Fe per
unit cell), rather than an isolated Fe atom, right? That is the chemical
potential reference for Fe that was used in calculating the 1.6 eV
formation energy value.</b> And for what it's worth I don't think point
defect calculations are that trivial.<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>3) thanks very much for the reference Rev. Mod. Phys. 86, 253 (2014).</div></div></blockquote><div><br></div><div style="font-family:arial,helvetica,sans-serif">Regarding chemical potential reference, see <b>section II.B.2 of this article</b>.</div></blockquote>
</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Best,<br></div><div><div dir="ltr" class="gmail-m_-7280164835633312346gmail-m_-5736710660860756931m_6975272543679907756gmail_signature"><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div><div><span style="font-family:arial,helvetica,sans-serif"><font size="2"><span style="color:rgb(102,102,102)"><b><span class="gmail_default" style="font-family:arial,helvetica,sans-serif">
</span></b></span></font></span><div style="font-family:arial,helvetica,sans-serif"><span class="gmail_default" style="font-family:arial,helvetica,sans-serif"></span>Kevin May, PhD<br></div><div style="font-family:arial,helvetica,sans-serif">Postdoctoral Associate</div><div style="font-family:arial,helvetica,sans-serif">Department of Materials Science and Engineering</div><div style="font-family:arial,helvetica,sans-serif">Massachusetts Institute of Technology</div>
<span style="font-family:arial,helvetica,sans-serif"></span><br><span style="font-family:arial,helvetica,sans-serif"></span></div></div><span style="font-family:arial,helvetica,sans-serif"></span><br><br><div><span style="font-family:arial,helvetica,sans-serif"><font size="2"><font size="1"><span style="color:rgb(102,102,102)"></span></font></font></span><span style="font-family:arial,helvetica,sans-serif"><font size="2"><font size="1"><span style="color:rgb(102,102,102)"></span></font></font></span></div></div></div></div></div></div></div><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Jun 18, 2019 at 11:54 AM mehrdad zamzamian <<a href="mailto:mehrdad.zamzamian@gmail.com" target="_blank">mehrdad.zamzamian@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr">Dear Kevin<div>Hi again</div><div>Sorry i bothered you many times for asking many questions, but i am really confused about my case</div><div>After using the paw-pp that you suggested, i obtained E(f-vacancy)~2.0 eV!! here in attachment, i gave my input. i used a 128-atom supercell for a perfect crystal (E=32199.76950786 Ry) and by removing a Fe atom, i had E=31870.37251766 Ry and isolated Fe E=329.18792433 Ry. It seems that i cannot obtain a better result than 2 eV. I appreciated if you give me any suggestions. the paper that you mentioned talked about "Ecorr". what exactly is this parameter?</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, Jun 1, 2019 at 11:27 PM Kevin May <<a href="mailto:kmay@mit.edu" target="_blank">kmay@mit.edu</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div dir="ltr" class="gmail_attr"><span class="gmail_default" style="font-family:arial,helvetica,sans-serif">Hi Mehrdad,</span></div><div dir="ltr" class="gmail_attr"><span class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></span></div><div dir="ltr" class="gmail_attr"><span class="gmail_default" style="font-family:arial,helvetica,sans-serif"></span>On Sat, Jun 1, 2019 at 1:58 PM mehrdad zamzamian <<a href="mailto:mehrdad.zamzamian@gmail.com" target="_blank">mehrdad.zamzamian@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">With regard<div>Dear Kevin</div><div>1) Actually, my reference is computational material science 44(2008) 690-694 (although they reported delta(E)= -0.456 eV/atom that i don't know what it is. because i said that it must be 1.6 eV according to <a href="https://doi.org/10.1080/09506608.2018.1560984" target="_blank">https://doi.org/10.1080/09506608.2018.1560984</a>). i also used spin-polarized (0.2 for Fe) but the same result was obtained (not better than 2.2 eV). I also used constant volume (by using relax calculation not vc_relax), but i had the same results.</div></div></blockquote><div><br></div><div style="font-family:arial,helvetica,sans-serif">The first paper you mention does not calculate vacancy formation energy, the -0.456 eV/atom is the bulk formation energy of orthorhombic Fe3C from GGA. The second paper is a review article that cites the paper by Jiang et al. that I mentioned in my last email for their ~1.6 eV formation energy of a Fe vacancy.<br></div><div style="font-family:arial,helvetica,sans-serif"></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>2) thanks for the proposed links, but in that reference they offered two non-consistent pps (C.pbe-n-kjpaw_psl.1.0.0.UPF and Fe.pbe-spn-kjpaw_psl.0.2.1.UPF) that i cannot use for Fe3C. i used these pp:</div><div>C.pbe-n-rrkjus_psl.1.0.0.UPF<br></div><div><span class="gmail_default" style="font-family:arial,helvetica,sans-serif"></span>Fe.pbe-spn-rrkjus_psl.1.0.0.UPF<br></div></div></blockquote><div><br></div><div style="font-family:arial,helvetica,sans-serif">I'm not sure what you mean by "non-consistent", or why you can't use those PAW datasets for your calculation. If you need to use ultrasoft for another reason, I'd still recommend using Fe.pbe-spn-rrkjus_psl.0.2.1.UPF instead of the psl.1.0.0 version. <br></div><div style="font-family:arial,helvetica,sans-serif"><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div></div><div>I am really confused about how can i calculate this rather simple parameter. i should mention that i calculate the Fe vacancy with:</div><div>E(Fe-vacancy)=E(perfect Fe3C)- E(Fe3C with lack of one Fe atom)- E(single Fe)</div></div></blockquote><div><br></div><div style="font-family:arial,helvetica,sans-serif"><span class="gmail_default" style="font-family:arial,helvetica,sans-serif"></span>By E(single Fe) you mean 1/2 the energy of ferromagnetic BCC Fe (2 Fe per unit cell), rather than an isolated Fe atom, right? That is the chemical potential reference for Fe that was used in calculating the 1.6 eV formation energy value. And for what it's worth I don't think point defect calculations are that trivial.<br></div><div style="font-family:arial,helvetica,sans-serif"></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>3) thanks very much for the reference Rev. Mod. Phys. 86, 253 (2014).</div></div></blockquote><div><br></div><div style="font-family:arial,helvetica,sans-serif">Regarding chemical potential reference, see section II.B.2 of this article.<br></div><div style="font-family:arial,helvetica,sans-serif"><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div><br></div><div><div>regards</div><div><br></div><div><div style="color:rgb(80,0,80)">Seyed Mehrdad Zamzamian</div><div style="color:rgb(80,0,80)">Sharif University of Technology, Tehran, Iran</div><div style="color:rgb(80,0,80)">Energy engineering department</div><div>E-mail: <a href="mailto:mehrdad.zamzamian@gmail.com" target="_blank">mehrdad.zamzamian@gmail.com</a><span class="gmail_default" style="font-family:arial,helvetica,sans-serif"></span></div></div></div></div></blockquote><div><span class="gmail_default" style="font-family:arial,helvetica,sans-serif"></span></div><div><span class="gmail_default" style="font-family:arial,helvetica,sans-serif">Good luck,</span></div><div><span class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br>
</span></div><div><div style="font-family:arial,helvetica,sans-serif"><span class="gmail_default" style="font-family:arial,helvetica,sans-serif"></span>Kevin May, PhD<br></div><div style="font-family:arial,helvetica,sans-serif">Postdoctoral Associate</div><div style="font-family:arial,helvetica,sans-serif">Department of Materials Science and Engineering</div><div style="font-family:arial,helvetica,sans-serif">Massachusetts Institute of Technology</div><span class="gmail_default" style="font-family:arial,helvetica,sans-serif"></span><br></div></div></div>
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