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Re: The awful message at all real frequencies from hessian

Alex Granovsky


By definition, the stationary point is any point on PES
that has zero energy gradient. This property is not
related with the number of real and imaginary frequencies.
E.g., any saddle point is the stationary point as well.

This message arises because the gradient-related criteria
used to decide whether the geometry optimization process
successfully converged or not are not exactly the same as
the criteria used by the Hessian code to check optimized geometry
for small gradient.

In most cases this message can be safely ignored. In the case
of very flexible, non-rigid molecules, one may need to perform
additional geometry optimization using tighter opttol value.

Alex Granovsky

On Mon Nov 16 '09 1:41am, Alexandr wrote
>   I count hessian and frequencies.
>   The molecule structure has been preliminary optimised in the same basis. However has received in a mourning framework the message of the program which dreams in dreadful dreams to beginners who master FireFly - THIS IS NOT A STATIONARY POINT ON THE MOLECULAR PES. THE VIBRATIONAL ANALYSIS IS NOT VALID!!!
>   But after all ALL frequencies are real! The result of optimisation of geometry of a molecule is estimated after absence of imaginary frequencies, instead of under messages of certainly remarkable program FireFly! (By the way, I suggest so to write the program name - through two capital letters).      
> Why so it has turned out?
> I attach file OUTPUT.
> Thanks in advance!


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