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 >
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