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
_______________________________________________________________________________
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worldwide who are victims of terrorism, military aggression, and indiscriminate
warfare.
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