[QE-users] vacancy formation energy

[Giuseppe Mattioli]

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)
>> Mob (*preferred*) +39 373 7305625
>> 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>