From owner-chemistry ^at^ ccl.net Tue Sep 2 16:26:00 2014 From: "Acioli, Paulo p-acioli|,|neiu.edu" To: CCL Subject: CCL:G: about electron affinity Message-Id: <-50466-140902132654-3411-l83xR0quMRdR1i/T7VXnyQ%a%server.ccl.net> X-Original-From: "Acioli, Paulo" Content-Type: multipart/alternative; boundary=e89a8f502e16be60270502186b0d Date: Tue, 2 Sep 2014 12:26:33 -0500 MIME-Version: 1.0 Sent to CCL by: "Acioli, Paulo" [p-acioli::neiu.edu] --e89a8f502e16be60270502186b0d Content-Type: text/plain; charset=UTF-8 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. Paulo Acioli, Chair Earth Science and Physics Associate Professor of Physics 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 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> > > --e89a8f502e16be60270502186b0d Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
You will always get negative electron binding energy at th= e HF level. Negative ions require correlation. Once you co to a post-HF met= hod, if your molecule can bind an electron, you should be able to obtain a = positive electron affinity.=C2=A0

Paulo Acioli, Chair Earth Science and Physics=C2=A0

Associate Professor of Physics=C2=A0

Departm= ent 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/departm= ents/physics

3D""



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=C2=A0 Archirel" [pierre.archirel~~u-psud.fr]
Dear colleagues,
I have a closed shell molecule (rather large: 12 first row atoms) and I wan= t 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 e= lectron is not bound and the SOMO built of the most diffuse gaussians of th= e basis.
The CCSD(T) and SAC-CI methods (which are affordable in my case) give a neg= ative electron affinity... but are these methods reliable? These methods us= e the HF orbitals, can they bind an electron if it is not bound at the HF l= evel?
Or shall I use CAS methods (very expansive in my case) which optimize orbit= als 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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