Hi Mehrdad, 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: https://www.crystallography.net/cod/9008536.cif). 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:
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. > >> 3) thanks very much for the reference Rev. Mod. Phys. 86, 253 (2014). >> > > Regarding chemical potential reference, see *section II.B.2 of this > article*. > Best, Kevin May, PhD Postdoctoral Associate Department of Materials Science and Engineering Massachusetts Institute of Technology On Tue, Jun 18, 2019 at 11:54 AM mehrdad zamzamian < [email protected]> wrote: > Dear Kevin > Hi again > Sorry i bothered you many times for asking many questions, but i am really > confused about my case > 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? > > On Sat, Jun 1, 2019 at 11:27 PM Kevin May <[email protected]> wrote: > >> Hi Mehrdad, >> >> On Sat, Jun 1, 2019 at 1:58 PM mehrdad zamzamian < >> [email protected]> wrote: >> >>> With regard >>> Dear Kevin >>> 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 >>> https://doi.org/10.1080/09506608.2018.1560984). 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. >>> >> >> 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. >> >>> 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: >>> C.pbe-n-rrkjus_psl.1.0.0.UPF >>> Fe.pbe-spn-rrkjus_psl.1.0.0.UPF >>> >> >> 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. >> >> I am really confused about how can i calculate this rather simple >>> parameter. i should mention that i calculate the Fe vacancy with: >>> E(Fe-vacancy)=E(perfect Fe3C)- E(Fe3C with lack of one Fe atom)- >>> E(single Fe) >>> >> >> 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. >> >>> 3) thanks very much for the reference Rev. Mod. Phys. 86, 253 (2014). >>> >> >> Regarding chemical potential reference, see section II.B.2 of this >> article. >> >> >>> regards >>> >>> Seyed Mehrdad Zamzamian >>> Sharif University of Technology, Tehran, Iran >>> Energy engineering department >>> E-mail: [email protected] >>> >> Good luck, >> >> Kevin May, PhD >> Postdoctoral Associate >> Department of Materials Science and Engineering >> Massachusetts Institute of Technology >> >>
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