[QE-users] Negatively charged isolated molecule

[Ernane de Freitas Martins]

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.mattioli at 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 minimize this latter source of error by using a
> hybrid GGA-EXX functional such as B3LYP, where the non local
> Hartree-Fock part of the exchange functional can recover part of the
> delocalization error, but you are not free yet from the instability of
> carbonate in gas phase.
> HTH
> Giuseppe
>
> Ernane de Freitas Martins <ernanefmg at gmail.com> ha scritto:
>
> > Hello,
> >
> > I'm experiencing a problem to run a negatively charge molecule in quantum
> > espresso. The system is CO32-.
> >
> > I try both vacuum and solvated (environ) calculations. The solvated one
> > works fine.
> >
> > The problem is the calculation in vacuum. It never give the first ionic
> > step because the SCF accuracy never reaches the convence criterion.
> >
> > I tried many different solutions (increase cutoffs and box size, use
> assume
> > isolated, decreasing and changing the mixing scheme and etc) and nothing
> > works.
> >
> > The unique calculation that works fine for vacuum is the one with a box
> > size of 7.9 x 7.9 x 7.9 A. I really don't understand why it only works
> for
> > this specific box size.
> >
> > I ran several other charged systems (+1, +2 and -1 total charge) and all
> of
> > them worked fine. The problem appears for -2 total charge in vacuum.
> >
> > Would some of you kindly help me in this?
> >
> > Cheers,
> >
> > Dr. Ernane de Freitas Martins
> > Postdoctoral researcher
> > IF - USP
> > São Paulo, SP - Brazil
>
>
>
> 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: <giuseppe.mattioli at ism.cnr.it>
>
> _______________________________________________
> users mailing list
> users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20190315/586c49b9/attachment.html>