[QE-users] vacancy formation energy

[mehrdad zamzamian]

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?

Thanks

Seyed Mehrdad Zamzamian
Sharif University of Technology, Tehran, Iran
Energy engineering department
E-mail: mehrdad.zamzamian at gmail.com

On Fri, May 10, 2019 at 1:07 AM Giuseppe Mattioli <
giuseppe.mattioli at ism.cnr.it> wrote:

>
> The difference is now at least reasonable. The remaining discrepancy
> may be due to a different computational setup used in your reference
> (xc functional, pseudopotentials, cutoff, ...). It is not possible to
> say more than this without seeing your setup and the reference setup.
> HTH
> Giuseppe
>
> Quoting mehrdad zamzamian <mehrdad.zamzamian at gmail.com>:
>
> > Thanks for considering to my case
> > I calculated the isolated Fe in a BCC crystal: E= -55.74720381 Ry
> > again i have
> > total energy of 64 atoms= -2860.35431865 Ry
> > total energy of 63 atoms (removing a Fe atom)= -2804.44525448 Ry
> > so, E(vacancy)=-2860.35431865+2804.44525448+55.74720381= -0.16186Ry=2.2
> eV!
> > This time it was so closer to 1.6 eV, but it still has almost 37% error!!
> > I checked various configurations for isolated Fe (changing magnetization,
> > E_cut, cell size and...) but the best result was this 2.2 eV.
> > I appreciate any suggestions.
> > Thanks
> >
> > Seyed Mehrdad Zamzamian
> > Sharif University of Technology, Tehran, Iran
> > Energy engineering department
> > E-mail: mehrdad.zamzamian at gmail.com
> >
> >
> > On Thu, May 9, 2019 at 3:25 PM Giuseppe Mattioli <
> > giuseppe.mattioli at ism.cnr.it> wrote:
> >
> >>
> >> Dear Mehrdad Zamzamian
> >> Please sign always your posts to the forum with name and scientific
> >> affiliation, we appreciate it.
> >> I suppose that the error is in the calculation of the single Fe atom.
> >> You should calculate the formation energy with respect to the
> >> reference energy of a Fe atom in its standard state, that is the bcc
> >> crystal.
> >> HTH
> >> Giuseppe
> >>
> >> Quoting mehrdad zamzamian <mehrdad.zamzamian at gmail.com>:
> >>
> >> > with regard
> >> > I want to calculate vacancy formation energy in Fe3C. I calculated the
> >> > following results by using these two pp:
> >> > Fe     55.84500  Fe.pbe-nd-rrkjus.UPF
> >> > C      12.01070  C.pbe-rrkjus.UPF
> >> > total energy of 64 atoms= -2860.35431865 Ry
> >> > total energy of 63 atoms (removing a Fe atom)= -2804.44525448 Ry
> >> > total energy of a single Fe atom= -55.45181620 Ry
> >> > using two ways i can calculate:
> >> > the first one) E(vacancy)= -2804.44525448 +(63/64)*2860.35431865
> >> > =11.21602794 Ry =152.60188965 eV!!!!!!
> >> > the second way) E(vacancy)= +2860.35431865-2804.44525448-55.45181620=
> >> > 0.45724797 Ry =6.2211778211 eV!!!!!!
> >> >
> >> > but in references, it must be ~1.61 eV ( and also i reached to this
> value
> >> > using MD simulation). what is wrong? Which calculation way is correct?
> >> >
> >> > Thanks
> >>
> >>
> >>
> >> GIUSEPPE MATTIOLI
> >> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
> >> Via Salaria Km 29,300 - C.P. 10
> >> I-00015 - Monterotondo Scalo (RM)
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> >> Tel + 39 06 90672342 - Fax +39 06 90672316
> >> E-mail: <giuseppe.mattioli at ism.cnr.it>
> >>
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>
>
>
> GIUSEPPE MATTIOLI
> CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
> Via Salaria Km 29,300 - C.P. 10
> I-00015 - Monterotondo Scalo (RM)
> Mob (*preferred*) +39 373 7305625
> Tel + 39 06 90672342 - Fax +39 06 90672316
> E-mail: <giuseppe.mattioli at ism.cnr.it>
>
> _______________________________________________
> Quantum Espresso is supported by MaX (www.max-centre.eu/quantum-espresso)
> users mailing list users at lists.quantum-espresso.org
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