From owner-chemistry -8 at 8- ccl.net Tue Sep 2 17:01:00 2014 From: "Igors Mihailovs igors.mihailovs0-x-gmail.com" To: CCL Subject: CCL:G: about electron affinity Message-Id: <-50467-140902133217-18661-ZHHJcmgC3+9rAcbpENCHvg,+,server.ccl.net> X-Original-From: Igors Mihailovs Content-Type: multipart/alternative; boundary=bcaec51869dcdb7f420502187fb9 Date: Tue, 2 Sep 2014 20:31:51 +0300 MIME-Version: 1.0 Sent to CCL by: Igors Mihailovs [igors.mihailovs0-#-gmail.com] --bcaec51869dcdb7f420502187fb9 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Dear Pierre, Which density functional do You use? Some of them might give quite reasonable results, whereas other might not, especially if your molecule contains long conjugated chain. 1 eV does not seem to be too few for me, but in no way I could say that I am high-valued professional in the field. There are sometimes artificial bound-electron states, then electron is placed in very high levels... HF eigenvalues are non-naturally positive in most cases, because at Hartree=E2=80=93Fock level electron correlation is not treated. CI and coupled-cluster methods solve this by using many-determinant wavefunctions, describing electron correlation via admixing of the excitated states to the ground state studied, so results You obtained from them (especially from CCSD(T) ) seem to be OK in most cases (if You have used basis set that is sufficiently large). Is the bound electron on some very high level also in CCSD(T) and CI case? If yes, this may indeed be the effect of artificial binding... Regards, Igors Mihailovs, Institute of Solid State Physics, University of Latvia 2014-09-02 19:15 GMT+03:00 Pierre Archirel pierre.archirel++u-psud.fr < owner-chemistry . ccl.net>: > > 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 metho= ds > 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 > > > > -=3D This is automatically added to each message by the mailing script = =3D-> > > --bcaec51869dcdb7f420502187fb9 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Dear Pierre,

Which density functional d= o You use? Some of them might give quite reasonable results, whereas other = might not, especially if your molecule contains long conjugated chain. 1 eV= does not seem to be too few for me, but in no way I could say that I am hi= gh-valued professional in the field. There are sometimes artificial bound-e= lectron states, then electron is placed in very high levels...

HF eigenvalues are non-naturally positive in most cases= , because at Hartree=E2=80=93Fock level electron correlation is not treated= . CI and coupled-cluster methods solve this by using many-determinant wavef= unctions, describing electron correlation via admixing of the excitated sta= tes to the ground state studied, so results You obtained from them (especia= lly from CCSD(T) ) seem to be OK in most cases (if You have used basis set = that is sufficiently large). Is the bound electron on some very high level = also in CCSD(T) and CI case? If yes, this may indeed be the effect of artif= icial binding...

Regards,
Igors Mihailovs,
Institute= of Solid State Physics,
University of Latvia



2014-09-02 19:15 GMT+03:00 Pierre Archir= el pierre.archirel++u-psud.fr <owne= r-chemistry . ccl.net>:

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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