Peng,
By specifying
guess=mix in a udft calculation (must specify "u" in the functional name, or
Gaussian will use restricted by default since it's a singlet), you can get
Gaussian to make the alpha and beta HOMOs 50:50 positive and negative linear
combinations of one another. This will usually converge to a so-called
broken-symmetry solution having an <S^2> value for the KS determinant of
1.0 more or less. One can interpret this either as the open-shell singlet
energy, or project out the triplet by the Ziegler-Noodleman-Yamaguchi sort of
approach.
IA paper of ours from a few years back specifically
addressed the different singlet states in substituted phenyl nitrenes -- see
Johnson, W. T. G.; Sullivan, M. B.; Cramer, C. J.
"meta and para Substitution Effects on the Electronic State
Energies and Ring-Expansion Reactivities of Phenylnitrenes" Int. J. Quantum
Chem. 2001, 85, 492..
Best
regards,
Chris
On Jul 10, 2009, at 12:40 PM, Huo-Lei Peng
huolei.peng166|-|gmail.com wrote: Thanks for your reply.
I'd like to do calculation on the open-shell singlet (not a triplet).
Open-shell(U) and restricted (R) calculations in Gaussian
gave me same results. So in Gaussian, how to set input to make two electrons in two different orbitals but we still have a singlet state?
Thanks.
Peng On Fri, Jul 10, 2009 at 11:14 AM, Jose Alberto Fernandes
jafernandes{:} ua.pt
<owner-chemistry**ccl.net> wrote:
Sent to CCL by: "Jose Alberto Fernandes"
[jafernandes=-=ua.pt]
Hello
I don't know if I understood your
problem. Lets try.
Please see the following excerpt this input:
#
rb3lyp/3-21g guess=check
The "r" before "b3lyp" means that you want a
close shell calculation. If you don't want electron pairing you have to put
"ub3lyp" instead of "rb3lyp".
You should remember that a closed shell
compound has always a spin=1, and in a open shell the spin is different from 1.
In the case of nitrene (R-N ?) you can have R-N paired (spin=1) and unpaired
(spin=3).
So in the case of pairing you shoul input:
------------------------
# rb3lyp/3-21g guess=check
comment
0 1
geometry
----------------------
If you want
unpairing you should input:
---------------------
# ub3lyp/3-21g
guess=check
comment
0 3
geometry
----------------------
If I haven't answered your question, please explain
better.
Best regards
Jose
>
"Huo-Lei Peng huolei.peng166(!)gmail.com" wrote:
>
> Sent to CCL by:
Huo-Lei Peng [huolei.peng166]=[gmail.com]
> --001636c5a4fb6b291a046e527474
>
Content-Type: text/plain; charset=ISO-8859-1
> Content-Transfer-Encoding:
7bit
>
> Hi, Dear All:
> I
have a question about calculation on the open-shell singlet using
>
Gaussian. For example, nitrene species may have an open-shell and closed
> shell singlets. In Gaussian, how to set the calculation to get open-shell
or
> closed-shell specifically? Thanks.
>
> Peng
>
> Content-Type:
text/html; charset=ISO-8859-1
> Content-Transfer-Encoding:
quoted-printable
>
> Hi, Dear
All:<div><br></div><div>I have a question about
calculation on the=
> open-shell singlet using Gaussian. For
example, nitrene species may have a=
> n open-shell and closed shell
singlets. In Gaussian, how to set the calcula=
> tion to get open-shell
or closed-shell specifically? Thanks.</div>
>
<div><br></div><div>Peng</div>
>
>
--001636c5a4fb6b291a046e527474--
>
>
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