From owner-chemistry.,at,.ccl.net Tue Sep  2 12:16:00 2014
From: "Pierre Archirel pierre.archirel++u-psud.fr" <owner-chemistry|-|server.ccl.net>
To: CCL
Subject: CCL:G: about electron affinity
Message-Id: <-50464-140902121505-899-8/D/dF8hDclIKDUE5T3HnA|-|server.ccl.net>
X-Original-From: "Pierre  Archirel" <pierre.archirel:+:u-psud.fr>
Date: Tue, 2 Sep 2014 12:15:04 -0400


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