Subject: summary: MO & state symmetry in G94/98

From: [email-masked] (Georg Schreckenbach)
Date: Fri, 26 Feb 1999 10:53:00 -0600

Dear CCL,

this is my summary regarding my question posted last week. I tried
to make GAUSSIAN determine the symmetry of the MOs in a DFT
calculation. The result, in short: it is not possible, at least not for my
molecule ([UO2Cl4]2-, D4h, with an ECP basis set on U.)
   I got a number of interesting suggestions, and I tried them all but nothing
helped. This seems to be an artefact of GAUSSIAN, and other programs
don't have the problem (e.g. ADF or Jaguar, cf. also answer #5 below.)

Here is what I did try (without success, as I said already)
- "Symm=Loose"
- "Conver=11", together with IntRep
- various finer integration grids
- fine integration grids combined with "SCF=(Conver=11, Intrep)
- "QC" combined with all of the above

Thanx to all who replied, and best regards,
Georg

-----------------------------------
The detailed answers:

#1: Original question:

Dear all,

while running a DFT single point on a symmetric (D4h) molecule
using Gaussian98, I get the message that the program is unable to
determine the symmetry of some orbitals, and consequently of the
electronic state. This is problematic since I try to calculate excited
states, and if the MO symmetries are unknown, then so are the
excited state symmetries.

Is there a reason for this behavior? Is there a way to make the program
find the appropriate symmetry labels for the orbitals? -- I tried already
SCF=(IntRep,Tight) but it had no effect.

Thank you very much! -- I'll summarize if there is any interest.

Best regards, Georg

-----------------------------------
#2

From: [email-masked]
Date: Mon, 22 Feb 1999 09:09:42 +0100

Dear Dr. Schreckenbach,

I would be very intersted in a summary. I once asked Doug Fox almost the
same question, but I never got a reply that enabled me to work my way
around the problem. I have a feeling that only thing one can to do is to
determine the symmetry of the state manually.

 All the best,

   Theis Soelling,

**  **  **      **  Mr. Theis Ivan Solling
**  **   ** ** **       Department of Chemistry
******    ******        University of Copenhagen
**  **      **          DK-2100 Copenhagen
**  **      **          Ph. 45-3532-0187/Fax. 45-3532-0212

-----------------------------------
#3

Date: Fri, 19 Feb 1999 17:07:57 -0600
From: John McKelvey <[email-masked]>

Is there a symmetry threshold value available? i.e. Symmetry is determined
by comparing ao coefficients. The "same" or "not the same" is measured by
how large the difference between the coefficients is... Just looked in the
manual... try SYMMETRY=LOOSE ....  You might say this is a workaround, but
the differences judged ma be of the order of 10**-5 or smaller.. is this
important?

John McKelvey
NCSA

-----------------------------------
#4

From: [email-masked]
Date: Mon, 22 Feb 1999 16:20:35 +0000 (CUT)

Hello Georg,

we've had a similar problem. It was solved by doing a very tight
SCF-Calculation. We used scf=(conver=11,intrep) and the unresolved
orbitals become nice.

Good luck

Alex

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-----------------------------------
#5

From: George Vacek <[email-masked]>
Date: Wed, 24 Feb 1999 13:39:05 -0800 (PST)

Georg,

%% using Gaussian98, I get the message that the program is unable to
%% determine the symmetry of some orbitals, and consequently of the
%% electronic state.

I'm not sure why Gaussian has this problem.  It has been around since
the early days of Gaussian (certainly 92, most probably earlier).
Maybe it is an artifact of the fact that the early versions of
Gaussian didn't use symmetry at all.  In principal orbital symmetry
identification is something that is easy to do right.  We've gotten
compliments on our Jaguar program because it does properly identify
orbital symmetry and everyone is used to the crappy behaviour of
Gaussian.

Regards,
George

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