From owner-chemistry %-% at %-% ccl.net Wed Feb 4 23:51:02 2009 From: "Sue Lam chsue2004#,#yahoo.com" To: CCL Subject: CCL:G: Broken Symmetry Singlet Excited State Message-Id: <-38555-090204224142-10972-7LRjA6x37X9Brs2cSjYLPg**server.ccl.net> X-Original-From: Sue Lam Content-Type: multipart/alternative; boundary="0-712308165-1233801683=:21903" Date: Wed, 4 Feb 2009 18:41:23 -0800 (PST) MIME-Version: 1.0 Sent to CCL by: Sue Lam [chsue2004**yahoo.com] --0-712308165-1233801683=:21903 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Hello Chris, =A0 Thank you very much for your reply. I am studying a reaction, in which the = transition state=A0contain biradical character. I=A0have tired=A0to extract= the energy of the pure singlet from the broken symmetry state by using the= spin-correction procedure which was proposed by Yamaguchi et al (Chem. Phy= s. Lett. 1994, 231, 25=9633) =A0 E(singlet) =3D E(broken symmetry from UDFT) + fSC[E(broken symmetry from UD= FT =96 E(triplet from UDFT)) =A0 Where fSC =3D 1 / [3 - 1] =A0 S^2: expectation value of the total spin =A0 The S^2 before and after the annihilation are listed in the Gaussian output= . In my case,=20 =A0 Annihilation of the first spin contaminant: S^2 before annihilation=A0=A0=A0=A0 0.8631,=A0=A0 after=A0=A0=A0=A0 0.4136 =A0 I am not sure that whether I should use the S^2 before or after the annihil= ation for the projection method.=20 =A0 Best regards, Sue --- On Wed, 2/4/09, Cristian V. Diaconu cvdiaconu!A!rice.edu wrote: > From: Cristian V. Diaconu cvdiaconu!A!rice.edu Subject: CCL:G: Broken Symmetry Singlet Excited State To: "L, Sue " Date: Wednesday, February 4, 2009, 2:15 PM Sent to CCL by: "Cristian V. Diaconu" [cvdiaconu~!~rice.edu] Hello Sue, The total energy reported by Gaussian is not for 'annihilated' wave function, but for the single determinant that it uses in the Kohn-Sham sche= me (for DFT there isn't really any wave function). There are ways to extract the energy of the pure singlet from the broken symmetry state, but for DFT = they only work in certain cases. Please look at discussions in: J. Chem. Phys. 121, 10026 (2004) J. Chem. Phys. 74, 5737 (1981) Coord. Chem. Rev. 238=96239, 187 (2003) C. J. Cramer, in Essentials of Computational Chemistry. Theories and Models= . (Wiley, Chichester, 2002), Chap. 14.4, pp. 456 =96 459. For example, for a molecule with two unpaired electrons on two sites which interact weakly (e.g., H2 molecule stretched, with a large bond length, say= 10 Angstroms), if ~ 1, E(singlet) =3D 2 E(broken sym) - E(triplet) I hope this helps. If you have further questions, please include a little detail on the system you are looking at. Best regards, Chris Sue L chsue2004(~)yahoo.com wrote: > Sent to CCL by: "Sue L" [chsue2004..yahoo.com] > Hi,=20 > I am running a DFT open-shell singlet calculation using Gaussian 03 to obtain a broken symmetry singlet excited state. Does anyone know whether th= e electronic energy calculated at the end based on the annihilated wave funct= ion or not?=20 > Thank you very much! >=20 > Best regards, > Sue>=20 >=20 >=20 -- Cristian V. Diaconu Postdoctoral Research Associate Department of Chemistry - MS60 Rice University PO Box 1892 Houston, TX 77251-1892 Phone: 713-348-3734 Email: cvdiaconu-x-rice.edu -=3D This is automatically added to each message by the mailing script =3D-http://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt=0A=0A=0A --0-712308165-1233801683=:21903 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: quoted-printable

Hello Chris,

 

Thank you very much for = your reply. I am studying a reaction, in which the transition state co= ntain biradical character. I have tired to extract the energy of = the pure singlet from the broken symmetry state by using the spin-correctio= n procedure which was proposed by Yamaguchi et al (Chem. Phys. Lett. 1994, 231, 25=9633)

 

E(singlet) =3D E(broken symmet= ry from UDFT) + fSC[E(broken symmetry from UDFT =96 E(triplet from UDFT))

 

Where fSC =3D 1<S^2> / [= 3<S^2> - 1<S^2>]

 

S^2: expectation value of the = total spin

 

The S^2 before and after the a= nnihilation are listed in the Gaussian output. In my case,

 

Annihilation of the firs= t spin contaminant:

S^2 before annihilation     0.8631,   after     0.4136

 

I am not sure that whether I s= hould use the S^2 before or after the annihilation for the projection metho= d.

 

Best regards,

Sue

--- On= Wed, 2/4/09, Cristian V. Diaconu cvdiaconu!A!rice.edu <owner-chem= istry]|[ccl.net> wrote:

From: Cristian V. Diaconu cvdiaconu!A!rice.edu <ow= ner-chemistry]|[ccl.net>
Subject: CCL:G: Broken Symmetry Singlet Excite= d State
To: "L, Sue " <chsue2004]|[yahoo.com>
Date: Wedne= sday, February 4, 2009, 2:15 PM

Sent to CCL by: "Cristian V. Di=
aconu" [cvdiaconu~!~rice.edu]
Hello Sue,

The total energy reported by Gaussian is not for 'annihilated' wave
function, but for the single determinant that it uses in the Kohn-Sham sche=
me
(for DFT there isn't really any wave function).  There are ways to extract
the energy of the pure singlet from the broken symmetry state, but for DFT =
they
only work in certain cases.  Please look at discussions in:

J. Chem. Phys. 121, 10026 (2004)
J. Chem. Phys. 74, 5737 (1981)
Coord. Chem. Rev. 238=96239, 187 (2003)
C. J. Cramer, in Essentials of Computational Chemistry. Theories and Models=
.
(Wiley, Chichester, 2002), Chap. 14.4, pp. 456 =96 459.

For example, for a molecule with two unpaired electrons on two sites which
interact weakly (e.g., H2 molecule stretched, with a large bond length, say=
 10
Angstroms), if <S^2> ~ 1,

E(singlet) =3D 2 E(broken sym) - E(triplet)

I hope this helps.  If you have further questions, please include a little
detail on the system you are looking at.

Best regards,
Chris

Sue L chsue2004(~)yahoo.com wrote:
> Sent to CCL by: "Sue  L" [chsue2004..yahoo.com]
> Hi,=20
> I am running a DFT open-shell singlet calculation using Gaussian 03 to
obtain a broken symmetry singlet excited state. Does anyone know whether th=
e
electronic energy calculated at the end based on the annihilated wave funct=
ion
or not?=20
> Thank you very much!
>=20
> Best regards,
> Sue>=20
>=20
>=20

-- Cristian V. Diaconu
Postdoctoral Research Associate
Department of Chemistry - MS60
Rice University
PO Box 1892
Houston, TX 77251-1892
Phone: 713-348-3734
Email: cvdiaconu-x-rice.edu



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