[QE-users] Problem stabilizing a di-anionic molecule

[Christoph Wolf]

Dear Nicola,

Thanks a lot for the input - I will give it a read!

Chris

On Tue, 25 Feb 2025 at 16:31, Nicola Marzari <nicola.marzari at epfl.ch> wrote:

>
>
> Dear Chris,
>
>
> we discuss this problem quite extensively here:
> https://pubs.acs.org/doi/10.1021/acs.jctc.9b00552
>
> In addition, approximate DFT functionals do a poor job in describing
> these extra electrons, that are very delocalized (interestingly, CCSD(T)
> also struggles because the basis sets don't really extend far enough).
>
> So, not sure there are ideal solutions, and if what you get is actually
> accurate; Perdew-Zunger SIC applied only to the extra electrons could
> also help.
>
> Some of this is also discussed here, in terms of weakly dipole-bound
> electrons: https://pubs.acs.org/doi/10.1021/acs.jctc.6b00145 .
>
> But in general it's a tough problem, so don't expect a simple solution.
>
>                         nicola
>
>
>
>
> On 25/02/2025 02:44, Christoph Wolf wrote:
> > Dear all,
> >
> > I am facing a tricky system: I am trying to calculate the anion and di-
> > anion of a small polycyclic aromatic hydrocarbon system (~20-25 atoms).
> >
> > I am using ONCV PPs and B3LYP just for completeness.
> >
> > The neutral molecule is closed shell (66 electrons for example) and the
> > anion (67 e-) is a radical, both converge fast and to meaningful
> > results. However it seems almost impossible to me to stabilize the di-
> > anion (68 e-). A closed shell (total magnetic moment = 0) does not
> > converge at all, a bi-radical (mtot=2) converges numerically but the
> > resulting cell seems to have a lot of charge "outside the molecule" when
> > I calculate the charge difference between anion and di-anion (pp
> > plot_num =0 and then take the difference between two calculations). Also
> > the projwfc.x output for the di-anion has a lot of "nondescript" states:
> >
> >
> >   ==== e(  33) =    -4.37227 eV ====
> >      |psi|^2 = 0.985
> > ==== e(  34) =    -1.39249 eV ====
> >      |psi|^2 = 0.001
> > ==== e(  35) =    -1.07395 eV ====
> > ...
> > ==== e(  50) =    -0.36725 eV ====
> >      |psi|^2 = 0.933
> >
> >
> > Any trick to help the system localize the additional charge better?
> >
> > Any help or comment is as always much appreciated!
> >
> > Ciao!
> > Chris
> > --
> > Christoph Wolf
> > IBS Center for Quantum Nanoscience
> > Seoul, South Korea
> >
> > https://stm25.org/ <https://stm25.org/>
> >
> >
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>
> --
> ----------------------------------------------------------------------
> Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
> Director, National Centre for Competence in Research NCCR MARVEL, SNSF
> Laboratory Head, PSI Center for Scientific Computing, Theory, and Data
> Contact info and websites at http://theossrv1.epfl.ch/Main/Contact
>


-- 
Group Leader "Theory of Quantum Systems at Surfaces"
IBS Center for Quantum Nanoscience
Seoul, South Korea

-- 
 <https://stm25.org/>
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