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.marz...@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/> > > > > > _______________________________________________________________________________ > > The Quantum ESPRESSO Foundation stands in solidarity with all civilians > worldwide who are victims of terrorism, military aggression, and > indiscriminate warfare. > > > -------------------------------------------------------------------------------- > > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > > users mailing list users@lists.quantum-espresso.org > > https://lists.quantum-espresso.org/mailman/listinfo/users > > > -- > ---------------------------------------------------------------------- > 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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