From owner-chemistry:~at~:ccl.net Fri Jan 25 03:29:00 2013 From: "Ulrike Salzner salzner**gmail.com" To: CCL Subject: CCL:G: weakly bound electrons Message-Id: <-48131-130125032303-31687-nyLsWK86zf6yHin+yjOKHQ() server.ccl.net> X-Original-From: Ulrike Salzner Content-Type: multipart/alternative; boundary=e89a8ff2565674cb3104d418a29e Date: Fri, 25 Jan 2013 10:22:56 +0200 MIME-Version: 1.0 Sent to CCL by: Ulrike Salzner [salzner|-|gmail.com] --e89a8ff2565674cb3104d418a29e Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Dear Pierre, many years ago I investigated the electron affinity of the methyl radical (Chem Phys Lett 1992,199,267). It is exactly such a case as you describe. In short: CCSD(T) is very good. With multireference methods and large basis sets, the electron might simply fly away. One has to be careful with diffuse functions if method does not get the anion bound. The electron will linger in a huge orbital far from the molecule. The best way is to use a reasonably large basis set and then crank up the level until the anion has the lower energy. Only then it makes sense to ask where the electron is. With the methyl anion it turned out that the largest contribution to the binding energy comes from zero point vibration! Regards, Ulrike On Thu, Jan 24, 2013 at 6:04 PM, Pierre Archirel pierre.archirel|-|u-psud.f= r wrote: > > Sent to CCL by: Pierre Archirel [pierre.archirel:-:u-psud.fr] > Dear colleagues, > What is the best method for calculating the small electron affinitiy > (say 0.01 - 0.10 eV) of a rather large system with many equivalent sites. > For my smallest system the valence CAS would require > 37 electrons in 36 orbitals, which is not feasible. > What about MP2, MP4 ? > Is CCSD(T) usable when the electron is not bound at the HF level? > I have gaussian 09 and Molpro available. > Thanks in advance. > > Pierre Archirel > LCP, Universite Paris-Sud, > Orsay, France > pierre.archirel!!u-psud.fr > > > ______________________________**______________________________**__ > > Pierre Archirel > Groupe Th=E9osim: Th=E9orie et Simulation > Laboratoire de Chimie Physique Tel: 01 69 15 63 86 > B=E2t 349 Fax: 01 69 15 61 88 > 91405 Orsay C=E9dex > France pierre.archirel(-)u-psud.fr > ______________________________**______________________________**__ > > > > -=3D This is automatically added to each message by the mailing script = =3D-> http://www.ccl.net/cgi-bin/**ccl/send_ccl_message http://www.ccl.net/cgi-bin/**ccl/send_ccl_message chemistry/announcements/**conferences/ > > Search Messages: http://www.ccl.net/chemistry/**searchccl/index.shtml http://www.ccl.net/spammers.**txt > > RTFI: http://www.ccl.net/chemistry/**aboutccl/instructions/ > > > --=20 Assoc. Prof. Ulrike Salzner Department of Chemistry Bilkent University 06800 Bilkent, Ankara --e89a8ff2565674cb3104d418a29e Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
Dear Pierre,
many years ago I inve= stigated the electron affinity of the methyl radical (Chem Phys Lett 1992,1= 99,267). It is exactly such a case as you describe. In short: CCSD(T) is ve= ry good. With multireference methods and large basis sets, the electron mig= ht simply fly away. One has to be careful with diffuse functions if method = does not get the anion bound. The electron will linger in a huge orbital fa= r from the molecule. The best way is to use a reasonably large basis set an= d then crank up the level until the anion has the lower energy. Only then i= t makes sense to ask where the electron is. With the methyl anion it turned= out that the largest contribution to the binding energy comes from zero po= int vibration!
Regards,
Ulrike


=
On Thu, Jan 24, 2013 at 6:04 PM, 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,
What is the best method for calculating the small electron affinitiy
(say 0.01 - 0.10 eV) of a rather large system with many equivalent sites. For my smallest system the valence CAS would require
37 electrons in 36 orbitals, which is not feasible.
What about MP2, MP4 ?
Is CCSD(T) usable when the electron is not bound at the HF level?
I have gaussian 09 and Molpro available.
Thanks in advance.

Pierre Archirel
LCP, Universite Paris-Sud,
Orsay, France
pierre.archirel!!u-psud.fr


_____________________________________________________________= _

=A0Pierre Archirel
=A0Groupe Th=E9osim: Th=E9orie et Simulation
=A0Laboratoire de Chimie Physique =A0 =A0 =A0Tel: 01 69 15 63 86
=A0B=E2t 349 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Fax: 0= 1 69 15 61 88
=A091405 Orsay C=E9dex
=A0France =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 pierre.archirel(-)u-psud.fr
_____________________________________________________________= _



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--
Assoc. Prof. Ulrike Sal= zner
Department of Chemistry
Bilkent University
06800 Bilkent, Ank= ara
--e89a8ff2565674cb3104d418a29e--