Thanks for your comments.
Yes, I din not request symmetry in my calculations. However, I also did not request symmetry in my DFT calculations with G16, the obtained geometry keeps the C2v symmetry. Acutally, in my previous calculations, I have not request any symmetry constraint and I had never enountered this problem. Thus, in my opinion, even if I did not request any symmetry, the optimized geometry should keep its symmetry, is it right? Thanks.
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.