Subject: Annihilation

From: Liu Xianghui <[email-masked]>
Date: Wed, 31 Jan 2001 23:12:20 +0800

Dear all
I also have questions about this.... :-)
That are some methods for spin correction for B3LYP.
The famous one is by K.Yamaguchi. 
"A spin correction procedure for unrestricted HF and MP wavefunctions for
singlet 
diradicals and polyradicals."(Chemical physics letters V149 537-542.)
Someone used it for spin correction for B3LYP. 
for example, E.Goldstein, K.N.Houk used it in "Density Fuctional Theory
prediction of Relative energies and istope effects for the concerted pathway
and stepwise pathway mechanism of the Diels-alder reaction of Butadiene and
ethylene" (J.AM.Chem.Soc. V118.No.25,1996. )
However, On page 6041, They said " Initial <S2> values for the diradical
stationary points(5-7)
range from 0.56 to 0.98 and become 0.07 and 0.23 after spin annihilation. "
I don't how this 0.07 and 0.23 come. 

For Gaussian output, there are S2, S2-1,S2A, what are they correspondingly? 

Thanks.         
 
Liu xianghui 

-----Original Message-----
From: Serguei Patchkovskii [mailto:[email-masked]]
Sent: Tuesday, January 30, 2001 7:13 AM
To: hu eric
Cc: [email-masked]
Subject: CCL:Annihilation

On Mon, 29 Jan 2001, hu eric wrote:
> In DFT singlet or triplet diradical g98 output, there's a S**2 after 
> annihilation. What is annihilation for? Does that mean I should use the
new 
> S**2 value as the reference? Thanks!

You should keep in mind that the "<S2>" expectation value, printed by 
Gaussian at the end of DFT calculations is not particularly meaningful 
in any case. This value is computed for the non-interacting Kohn-Sham 
reference wavefunction, and has no relation to the <S2> of the real, 
interacting system. The Gaussians' "<S2>" may be useful as a qualitative
indication of the degree of spin-contamination, but that's about it.

/Serge.P

---
Home page: http://www.cobalt.chem.ucalgary.ca/ps/

-= This is automatically added to each message by mailing script =-
[email-masked] -- To Everybody  | [email-masked] -- To Admins
[email-masked] -- HELP CHEMISTRY or HELP SEARCH
[email-masked] -- archive search    |    Gopher: gopher.ccl.net 70
Ftp: ftp.ccl.net  |  WWW: http://www.ccl.net/chemistry/   | Jan: [email-masked]