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

[Christoph Wolf]

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/>
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