[QE-users] Negatively charged isolated molecule

[Michal Krompiec]

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 <ernanefmg at 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.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>
>>
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