<div dir="ltr"><div dir="ltr">It seems the problem is XC functional type. I used the PBE with non-linear core correction USPP (Fe.pbe-nd-rrkjus.UPF). In literature, electron exchange and correlation are approximated using the Perdew and Wang PW91 formulation of the generalized gradient approximation (GGA) for the exchange-correlation functional, but i cannot find this PP in the site. Is there any way to have these PPs?</div><div dir="ltr"><br></div><div dir="ltr"><div>Thanks</div><div><br></div><div>Seyed Mehrdad Zamzamian</div><div>Sharif University of Technology, Tehran, Iran</div><div>Energy engineering department</div><div>E-mail: <a href="mailto:mehrdad.zamzamian@gmail.com" target="_blank">mehrdad.zamzamian@gmail.com</a></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, May 10, 2019 at 1:07 AM Giuseppe Mattioli <<a href="mailto:giuseppe.mattioli@ism.cnr.it">giuseppe.mattioli@ism.cnr.it</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"><br>
The difference is now at least reasonable. The remaining discrepancy <br>
may be due to a different computational setup used in your reference <br>
(xc functional, pseudopotentials, cutoff, ...). It is not possible to <br>
say more than this without seeing your setup and the reference setup.<br>
HTH<br>
Giuseppe<br>
<br>
Quoting mehrdad zamzamian <<a href="mailto:mehrdad.zamzamian@gmail.com" target="_blank">mehrdad.zamzamian@gmail.com</a>>:<br>
<br>
> Thanks for considering to my case<br>
> I calculated the isolated Fe in a BCC crystal: E= -55.74720381 Ry<br>
> again i have<br>
> total energy of 64 atoms= -2860.35431865 Ry<br>
> total energy of 63 atoms (removing a Fe atom)= -2804.44525448 Ry<br>
> so, E(vacancy)=-2860.35431865+2804.44525448+55.74720381= -0.16186Ry=2.2 eV!<br>
> This time it was so closer to 1.6 eV, but it still has almost 37% error!!<br>
> I checked various configurations for isolated Fe (changing magnetization,<br>
> E_cut, cell size and...) but the best result was this 2.2 eV.<br>
> I appreciate any suggestions.<br>
> Thanks<br>
><br>
> Seyed Mehrdad Zamzamian<br>
> Sharif University of Technology, Tehran, Iran<br>
> Energy engineering department<br>
> E-mail: <a href="mailto:mehrdad.zamzamian@gmail.com" target="_blank">mehrdad.zamzamian@gmail.com</a><br>
><br>
><br>
> On Thu, May 9, 2019 at 3:25 PM Giuseppe Mattioli <<br>
> <a href="mailto:giuseppe.mattioli@ism.cnr.it" target="_blank">giuseppe.mattioli@ism.cnr.it</a>> wrote:<br>
><br>
>><br>
>> Dear Mehrdad Zamzamian<br>
>> Please sign always your posts to the forum with name and scientific<br>
>> affiliation, we appreciate it.<br>
>> I suppose that the error is in the calculation of the single Fe atom.<br>
>> You should calculate the formation energy with respect to the<br>
>> reference energy of a Fe atom in its standard state, that is the bcc<br>
>> crystal.<br>
>> HTH<br>
>> Giuseppe<br>
>><br>
>> Quoting mehrdad zamzamian <<a href="mailto:mehrdad.zamzamian@gmail.com" target="_blank">mehrdad.zamzamian@gmail.com</a>>:<br>
>><br>
>> > with regard<br>
>> > I want to calculate vacancy formation energy in Fe3C. I calculated the<br>
>> > following results by using these two pp:<br>
>> > Fe 55.84500 Fe.pbe-nd-rrkjus.UPF<br>
>> > C 12.01070 C.pbe-rrkjus.UPF<br>
>> > total energy of 64 atoms= -2860.35431865 Ry<br>
>> > total energy of 63 atoms (removing a Fe atom)= -2804.44525448 Ry<br>
>> > total energy of a single Fe atom= -55.45181620 Ry<br>
>> > using two ways i can calculate:<br>
>> > the first one) E(vacancy)= -2804.44525448 +(63/64)*2860.35431865<br>
>> > =11.21602794 Ry =152.60188965 eV!!!!!!<br>
>> > the second way) E(vacancy)= +2860.35431865-2804.44525448-55.45181620=<br>
>> > 0.45724797 Ry =6.2211778211 eV!!!!!!<br>
>> ><br>
>> > but in references, it must be ~1.61 eV ( and also i reached to this value<br>
>> > using MD simulation). what is wrong? Which calculation way is correct?<br>
>> ><br>
>> > Thanks<br>
>><br>
>><br>
>><br>
>> GIUSEPPE MATTIOLI<br>
>> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA<br>
>> Via Salaria Km 29,300 - C.P. 10<br>
>> I-00015 - Monterotondo Scalo (RM)<br>
>> Mob (*preferred*) +39 373 7305625<br>
>> Tel + 39 06 90672342 - Fax +39 06 90672316<br>
>> E-mail: <<a href="mailto:giuseppe.mattioli@ism.cnr.it" target="_blank">giuseppe.mattioli@ism.cnr.it</a>><br>
>><br>
>> _______________________________________________<br>
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>><br>
<br>
<br>
<br>
GIUSEPPE MATTIOLI<br>
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA<br>
Via Salaria Km 29,300 - C.P. 10<br>
I-00015 - Monterotondo Scalo (RM)<br>
Mob (*preferred*) +39 373 7305625<br>
Tel + 39 06 90672342 - Fax +39 06 90672316<br>
E-mail: <<a href="mailto:giuseppe.mattioli@ism.cnr.it" target="_blank">giuseppe.mattioli@ism.cnr.it</a>><br>
<br>
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</blockquote></div>