On Thu, Sep 22, 2011 at 10:59 PM, Arne
Dieckmann adieckma^
googlemail.com <owner-chemistry#%#ccl.net> wrote:
Sent to CCL by: Arne Dieckmann [adieckma . googlemail.com]
I would not consider -1.9 wavenumbers an imaginary frequency. Have a look at the
Gaussian manual and whitepapers, there is a section about this issue.
Cheers,
Arne
On Sep 22, 2011, at 8:25 AM, Sam Abrash sabrash]_[richmond.edu wrote:
>
> Sent to CCL by: "Sam Abrash" [sabrash_+_richmond.edu]
> Hi Folks,
>
> I have a job involving hydrogen bonding of 3 acetylenes to the benzene
cation. I'm having trouble with the geometric convergence. I was
able to get the system to converge with normal convergence criteria,
opt=calcall, and MaxStep=5, but then I got an imaginary frequency of -1.9
wavenumbers.
>
> Subsequently, I changed to Opt=tight, tried both calcfc and calcall, and
have steadily reduced MaxStep to 1, but it still won't converge. The
force constant criteria have been met, but the problem is the displacement
criteria. Both this observation and looking at the structures with JMOL
show that the problem is finding the minimum in a very shallow potential.
>
> Two questions. First, is the 1.9 wavenumber imaginary frequency real
or an artifact? Second, any advice on how to force the system to converge?
Model chemistry is M062X/6-311++G**.
>
> Thanks!
> Sam>
>
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