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
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