Dear Gregory,
Gregory Geneste wrote:
I guess that charging a supercell (variable "netcharge") is performed,
as in other codes, that is, by suppressing the G=0 Fourier component of
the electrostatic potential to avoid divergence of the total energy
(tell me if I'm wrong...).
In the documentation of the code and in [Soler et al, J. Phys. Cond Matt
14 (2002), 2745], it is said that in that case, the Makov and Payne
correction is added automatically (only in the case of SC, BCC or FCC
cells).
Does it mean that using a charged cubic supercell, this correction is
taken into account in the total energy provided by the code (whatever a
molecule with vacuum around or a bulk supercell) ?
As you say, Siesta will add the compensating jellium background to avoid
divergence of the Coulomb energy.
Concerning the correction, the Madelung term of the Makov and Payne
correction (notice that the correction proposed by Makov and Payne
include also a self-consistent quadrupole term that is *not* calculated
in Siesta) is calculated and taken into account if you have a SC, BCC or
FCC cell *and* your system is a molecule.
If the system is not a molecule Siesta cannot calculate the Madelung
correction because it has to be scaled with the dielectric constant of
the material (see Makov and Payne paper) and Siesta simply doesn't know
it. A shortcut is running a fake calculation with the same cell shape
and a molecule in it (the Madelung correction solely depends on the cell
shape and not on its content), then scale it manually with an
appropriate dielectric constant (experimental, calculated,...) and add
it manually to your real calculation.
What is easy is knowing if Siesta has calculated and taken into account
the Madelung correction or not. If your system is charged and, for
whatever reason, Siesta cannot calculate the correction, you'll get a
big WARNING when it begins the first self-consistency cycle.
Riccardo
--
Riccardo Rurali
Escola Tècnica Superior d'Enginyeria (ETSE)
Universitat Autònoma de Barcelona (UAB)
Campus de la UAB
08193 Bellaterra (Barcelona)
Spain
tel.: +34 93 581 3531
fax.: +34 93 581 2600
e-mail: riccardo.rur...@uab.es
Man, the dope's that there's still hope
