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Alex Granovsky
gran@classic.chem.msu.su

this is most likely the manifestation of a problem known as
the "Pseudo Jahn-Telller effect". See papers and reviews by
I. B. Bersuker on this:

https://scholar.google.com/citations?user=maHGAPQAAAAJ&hl=en&oi=sra

In most cases these effects are caused by incompleteness of
active space or poor orbital basis, or both.

Hope this helps.

Kind regards,
Alex Granovsky





On Wed Dec 6 '17 4:15pm, Panwang Zhou wrote
-------------------------------------------
>Dear Pedro Silva,

>I have tried to request the C2v symmetry in DATA deck and set NOSYM=0 in the control section, however, it seems that this did not take effect, because from the second step, the geometry has changed the symmetry.

>On Mon Dec 4 '17 4:47pm, Pedro Silva wrote
>------------------------------------------
>>>Dear Panwang Zhou,

>>Your output states that you did not request C2v symmetry in the optimization algorithm. In your DATA deck, you should replace the C1 line by "Cnv  2" , followed by a blank line and by your geometry, suitably rotated/translated/etc to comply with the internal master frame detection conventions:

>>By default, the 'master frame' assumes that
>>1. z is the principal rotation axis (if any),
>>2. x is a perpendicular two-fold axis (if any),
>>3. xz is the sigma-v plane (if any), and
>>4. xy is the sigma-h plane (if any).
>>Use the lowest number rule that applies to your molecule.
>>
>>
>>Some programs (eg. ChemCraft) allow you to select the symmetry and automatically generated properly-formatted $DATA groups to ensure that your computation does not face trouble because of deficient adherence to those conventions.

>>