Dear Ernane
Is there a way of estimating this Jellium contribution and somehow discount
it from the total energy?
Is this necessary?
Periodic boundary conditions are fantastic for a lot of things (FFT,
plane waves, scaling, etc,), but particular care, which is not
necessary in the case of typical GTO calculations, must be given to
the calculation of electrostatic energy. In particular, the efficient
Ewald partition of Coulomb interactions in PBC diverges in the case of
charged species. a diffuse countercharge (aka jellium) is therefore
necessary, but it is also a source of error, as shown by Makov and
Payne a lot of time ago.
The assume isolated schemes deal with this and already provide a correct
energy?
There are a lot of correction schemes, but AFAIK it is not possible to
calculate "additive" total energy values in PBC for charged species,
that is, additive in the sense that the energy difference of A and A+
calculated in a given supercell is a meaningful estimate of the
ionization energy of A.
If you want to read something, this (and the references therein) may
be a good starting point
PHYSICAL REVIEW B 77, 115139, 2008
HTH
Giuseppe
Ernane de Freitas Martins ha scritto:
Dear all,
regarding energy calculations of charged systems in general, I also have
doubts about the Jellium contribution to the total energy. The unique
mention to Jellium I found is the phrase in the input description saying
that a background Jellium is added for charged calculations. Thus I have
some doubts.
Is there a way of estimating this Jellium contribution and somehow discount
it from the total energy?
Is this necessary?
The assume isolated schemes deal with this and already provide a correct
energy?
As I have mentioned, I didn't find further information about Jellium in QE
documentation.
Could some one clarify that to us or suggest a paper on this?
Cheers,
Dr. Ernane de Freitas Martins
Postdoctoral researcher
IF - USP
São Paulo, SP - Brazil
Em seg, 18 de mar de 2019 06:28, Laurens Siemons
escreveu:
Dear QE-users,
I always thought that it is not correct to calculate energies of isolated
ionic species under PBC due to the introduction of a Jellium background
inside the vacuum which has physically no meaning. But after reading this
post I assume that I am wrong and that you can perform calculations on
ionic species in a vacuum with QE?
With kind regards,
Laurens Siemons
PhD, UAntwerp (Belgium)
--
*Van:* users namens Nattino
Francesco
*Verzonden:* zaterdag 16 maart 2019 9:02
*Aan:* Quantum Espresso users Forum
*Onderwerp:* Re: [QE-users] Negatively charged isolated molecule
Dear Ernane,
As Giuseppe already pointed out, many anionic species are actually
unbound with standard density functionals. The continuum solvation model
helps to achieve convergence because the dielectric embedding stabilizes
the localized electronic configuration.
A way to circumvent the issue and to obtain the energy of carbonate in
vacuum could be the following: you calculate the energy of the system for
decreasing values of the dielectric constant and you extrapolate the energy
to the vacuum dielectric constant (epsilon=1).
Best regards,
Francesco Nattino,
EPFL
On Mar 15, 2019 7:30 PM, Michal Krompiec
wrote:
Dear Ernane,
Have you thought of using a more sophisticated method (like GW) on [CO3]-
to calculate its EA? This would give you the energy of [CO3]2- in vacuum.
Best,
Michal Krompiec
University of Southampton & Merck KGaA
On Fri, 15 Mar 2019 at 18:22, Ernane de Freitas Martins <
ernane...@gmail.com> wrote:
Dear Giuseppe,
I really appreciate your answer. Thank you very much for using your time
to answer my question.
I'll think on your suggestion about trying hybrid functionals. The point
is that I need to estimate the solvation energy for carbonate ion using the
environ module, then I'll need to run a vacuum calculation using the same
functional I'm already using rVV-10).
Thank you again for replying.
Atenciosamente,
Dr. Ernane de Freitas Martins
Postdoctoral researcher
IF - USP
São Paulo, SP - Brazil
Em sex, 15 de mar de 2019 15:04, Giuseppe Mattioli <
giuseppe.matti...@ism.cnr.it> escreveu:
Dear Ernane
Your question contains part of the answer! Carbonate ion (CO3 2-) is
not stable outside water, and calculations of its properties in gas
phase are likely not so meaningful, but in the case of model
thermodynamics cycles (e.g. Born-Haber). The excess negative charge is
unbound when not stabilized by a strongly polar solvent, and this is
likely responsible for instabilities in the construction of the
Kohn-Sham potential along scf iterations. Moreover, this happens on
top of the strong delocalization error you experience when you use a
standard GGA exchange-correlation functional, when the
self-interaction of strongly localized electrons in the J[n] Coulomb
potential is not cancelled by a same term in the semi local exchange
potential. You may
