[CP2K-user] [CP2K:11870] Is it necessary to perform frequency calculations for the optimized geometry in cp2k?

[Kee Choon Wee]

Hi Shakiba,

The purpose of a frequency calculation is to verify that the stationary
point you found is not a saddle point (1 imaginary frequency, i.e a TS) or
higher-order saddle point with (>1 imaginary frequency).
I don't think it has anything to do with getting struck in a local minima,
In fact, if you have no imaginary frequency the structure you found is a
minima (could be a global/local one).
You can try a short MD to see if there is a large transition within say a
picosecond, this might give you a hint as to whether it is a minima or
transition state.


On Mon, Jun 10, 2019 at 8:32 PM Mohammad Shakiba <
mshakiba.... at gmail.com> wrote:

> Hello everyone,
>
> When optimizing with CP2K, we set a force limit and a maximum step size
> (for example less than 10meV and 0.002Bohr) and when the calculations
> reached those limits it is done. Before using CP2K I used Gaussian 09. When
> the geometry optimization was fully performed, I performed frequency
> calculation in order to check that there is no imaginary frequency so the
> optimization is not stuck in the local minima. However, when it came to big
> molecules, the rwf file tended to be hundreds of GB, so the calculations
> was not possible. Now, my question is:
>
>
> Is it necessary to perform frequency calculations (like phonon
> calculations using phonopy) for the optimized geometry in CP2K? I mean the
> BFGS algorithm for geometry optimization is guaranteed to not stuck in the
> local minima? For example my system contains a quantum dot with many
> organic ligands (near 300 atoms) and the optimization is fully performed
> but I don't know if it would be acceptable to allege that this is the
> optimum geometry!  To sum up: when can we say that this is optimum geometry
> for this specific geometry configuration?
>
> Thanks in advance.
>
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