CCL:G: about electron affinity



Also, it may be useful to note here that the electron affinity is usually negative for either rather small aromatic molecules and those containing electron-donating groups (sp2-N, too, in this case, because it has lone pair), whereas for aromatics with many fused rings and those having electron accepting groups usually have positive EAs.
The experimental results also may give controversial suggestions. For example, naphthalene has EA of â0.20 eV, a value from ETS experiment, according to [D. M. A. Vera and A. B. Pierini, Phys. Chem. Chem. Phys., 2004, 6, 2899â2903.], cited in the second paper suggested by Mr. Cook; but in [O. Dolgounitcheva,V. G. Zakrzewski and J. V. Ortiz,
J. Phys. Chem. A 1997 101 (45), 8554-8564] value for naphthalene from photoelectron spectra is +0.14 eV.

With best regards,
Igors Mihailovs
Institute of Solid State Physics,
University of Latvia



2014-09-03 4:47 GMT+03:00 Ronald Cook cookrl/atda.com <owner-chemistry[-]ccl.net>:
There are four papers that address positive and negative electron affinities and the latter two address the computation of negative electron affinities

1) Tozer, David J., and Frank De Proft. "Computation of the hardness and the problem of negative electron affinities in density functional theory." The Journal of Physical Chemistry A 109.39 (2005): 8923-8929.

2)De Proft, Frank, et al. "Calculation of negative electron affinity and aqueous anion hardness using KohnâSham HOMO and LUMO energies." Faraday discussions 135 (2007): 151-159.

3)Puiatti, Marcelo, D. Mariano A. Vera, and Adriana B. Pierini. "Species with negative electron affinity and standard DFT methods. Finding the valence anions." Physical Chemistry Chemical Physics 10.10 (2008): 1394-1399.

4)Puiatti, Marcelo, D. Mariano A. Vera, and Adriana B. Pierini. "In search for an optimal methodology to calculate the valence electron affinities of temporary anions." Physical Chemistry Chemical Physics 11.40 (2009): 9013-9024.

Ronald Cook
Principal Scientist
TDA Research, Inc.


On Tue, Sep 2, 2014 at 11:26 AM, Acioli, Paulo p-acioli|,|neiu.edu <owner-chemistry]_[ccl.net> wrote:
You will always get negative electron binding energy at the HF level. Negative ions require correlation. Once you co to a post-HF method, if your molecule can bind an electron, you should be able to obtain a positive electron affinity.Â

Paulo Acioli, Chair Earth Science and PhysicsÂ

Associate Professor of PhysicsÂ

Department of Physics and Astronomy

Northeastern Illinois University

5500 North St. Louis Avenue, Chicago, IL 60625

Phone: (773) 442-4733

p-acioli]^[neiu.edu


http://www.neiu.edu/academics/college-of-arts-and-sciences/departments/physics



On Tue, Sep 2, 2014 at 11:15 AM, Pierre Archirel pierre.archirel++u-psud.fr <owner-chemistry]^[ccl.net> wrote:

Sent to CCL by: "Pierre Archirel" [pierre.archirel~~u-psud.fr]
Dear colleagues,
I have a closed shell molecule (rather large: 12 first row atoms) and I want to know if this molecule can bind an electron.
DFT tells me "yes" with positive values of the electron affinity, in the range 0.5-1.0 eV according to the functional. I suspect that these values are false, or at least largely overestimated.
I now turn to ab initio methods, but I first see that at the HF level the electron is not bound and the SOMO built of the most diffuse gaussians of the basis.
The CCSD(T) and SAC-CI methods (which are affordable in my case) give a negative electron affinity... but are these methods reliable? These methods use the HF orbitals, can they bind an electron if it is not bound at the HF level?
Or shall I use CAS methods (very expansive in my case) which optimize orbitals at the CI level? Is it obligatory in this case?
Many thanks in advance,
Pierre Archirel
LCP, Universite Paris-Sud, Orsay, France



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