Hello,
in PRB 214103 (2003), for the Fe16C1 system (BCC iron with a carbon atom in an
octahedral site), the solution enthalpy at 0 K is defined as
H=E(Fe16C1)-E(Fe16)-E(C),
being E(C) the total energy per atom in graphite and the meaning of the other
ones is straightforward. They have obtained, with VASP, H=0.58 eV.
By using Siesta with a DZP-DZP basis for iron (with which I obtained a very
good agreement of the lattice parameter, vacancy formation energy, and cohesion
energy with respect to the literature) and DZP-DZ for carbon (with which the
cohesion energy of graphite is in agreement with the above mentioned reference
and the lattice parameter with the experimental one), and applying the same
equation above to the same system, I obtained H=0.30 eV. I guess the difference
between VASP's H and Siesta's one is due to the BSSE. Nevertheless, I did not
figure out how to apply the correction. If I replace E(Fe16) by E(Fe16+C_ghost)
and E(C) by E(C+Fe16_ghost), things become worst. Does anyone have any idea on
how apply a BSSE correction in this case?
Thanks in advance,
Roberto Veiga
