[QE-users] vacancy formation energy

[Giuseppe Mattioli]

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
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