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: [email protected] On Fri, May 10, 2019 at 1:07 AM Giuseppe Mattioli < [email protected]> 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 <[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]> > >> > >> _______________________________________________ > >> 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 > >> > > > > 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 >
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