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 <[email protected]>:
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: [email protected]
On Thu, May 9, 2019 at 3:25 PM Giuseppe Mattioli <
[email protected]> 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 <[email protected]>:
> 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)
Mob (*preferred*) +39 373 7305625
Tel + 39 06 90672342 - Fax +39 06 90672316
E-mail: <[email protected]>
_______________________________________________
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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: <[email protected]>
_______________________________________________
Quantum Espresso is supported by MaX (www.max-centre.eu/quantum-espresso)
users mailing list [email protected]
https://lists.quantum-espresso.org/mailman/listinfo/users
