[CP2K-user] [CP2K:11877] Is it necessary to perform frequency calculations for the optimized geometry in cp2k?

[Kee Choon Wee]

You are welcome.

Regards,
Choon Wee

On Sat, Jun 15, 2019 at 9:58 PM Mohammad Shakiba <
mshakiba.... at gmail.com> wrote:

> Dear Kee Chon Wee,
>
> Thank you so much for your help.
>
> On Tuesday, June 11, 2019 at 1:54:09 PM UTC+4:30, Kee Choon Wee wrote:
>>
>> 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 <msha... 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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