Subject: Problems with CCSD

From: Ruth Marie Tanner <[email-masked]>
Date: Tue, 11 Jul 2000 11:27:21 -0400 (EDT)

I am trying to do optimization and frequency jobs for simple
neutral and cation structures (such as H2BF) with CCSD and CCSD(T).
I have no problem getting optimized structures and frequencies using
B3LYP, MP2, and CCD methods.  I do realize that analytic energies and
analytic gradients are calculated with CCD and numerical gradients and
numerical frequencies are calculated with CCSD and CCSD(T).

Here is my problem. I optimize the structure using CCD and arrive at a
reasonable input structure for CCSD.  When I run the CCSD job (especially
for cation structures), I end up with the following error:

 Framework group  C1[X(BFH2)]
 Deg. of freedom    6
 Full point group                 C1      NOp   1
 Omega: Change in point group or standard orientation.

 Error termination via Lnk1e in C:\G98W\l202.exe.
 Job cpu time:  0 days  0 hours 21 minutes 17.0 seconds.
 File lengths (MBytes):  RWF=   65 Int=    0 D2E=    0 Chk=    6 Scr=    1

This error seems to suggest a change in symmetry, but for most of the
molecules that I am studying, the structures either have no symmetry or
an accepted symmetry.  Can anyone make a suggestion for getting CCSD and
CCSD(T) jobs to optimize for these relatively simple cation structures.

thanks,
Ruth

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Ruth Tanner 						[email-masked] 
PhD Candidate, Physical Chemistry			"Oh no, not again."
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From: "Stefan Fau" <[email-masked]>
Date: Tue, 11 Jul 2000 16:38:27 -0400

Hi Ruth,

I don't know an answer to your question, but why
don't you do your optimizations using analytical
gradients? It would make the calculations faster,
even for tetratomic molecules. Try ACES 2, I don't
know if other programs can do analytic CCSD(T)
gradients, too.

Stefan
______________________________________________________________________
Dr. Stefan Fau                    |      [email-masked]
Quantum Theory Project     |     (352) 392-6714
University of Florida
Gainesville, FL 32611-8435