[CP2K-user] [CP2K:16494] Re: Prevent Cell Geometry/Vectors From Changing

[fabia...@gmail.com]

No, for MD the ensemble type determines if the cell dimensions are fixed or 
not: 
https://manual.cp2k.org/cp2k-9_1-branch/CP2K_INPUT/MOTION/MD.html#ENSEMBLE
The cell only changes if you choose NPT, otherwise it is fixed.

Fabian

On Monday, 24 January 2022 at 08:46:45 UTC+1 lenardc... at gmail.com wrote:

> Thanks for feedback Fabian, I appreciate it. Does the above also apply to 
> AIMD simulations where you have the
> &MOTION
>   &GEO_OPT
>   &END
> &END
> section still included?
> On Thursday, January 20, 2022 at 2:20:26 PM UTC+2 fabia... at gmail.com 
> wrote:
>
>> Hi Lenard,
>>
>> in cp2k there are two types of optimizations, GEO_OPT and CELL_OPT. In 
>> GEO_OPT the lattice vectors are fixed and only the atomic positions are 
>> optimized. In a CELL_OPT both the lattice vactors and the atomic positions 
>> can be relaxed simultaneously.
>>
>> So if you don't want the box to change you need 
>> RUN_TYPE GEO_OPT 
>> and  the
>> &MOTION
>>   &GEO_OPT
>>   &END
>> &END
>> section.
>>
>> If the SCF does not converge the forces (and pressure) are probably very 
>> bad and thus the optimizer (e.g. BFGS) takes unreasonable steps. If the SCF 
>> does not converge you should probably stop the simulation and improve SCF 
>> stability.
>>
>> Cheers,
>> Fabian
>> On Thursday, 20 January 2022 at 05:50:59 UTC+1 lenardc... at gmail.com 
>> wrote:
>>
>>> Hi there. So, I've been doing a few geometry optimizations and I have 
>>> seen that for some of them, the cell vectors change, sometimes a bit other 
>>> times a lot. This especially happens when the SCF run is not converged 
>>> multiple times in a row. The thing is, I don't want the cell vectors to 
>>> change, I don't want the atoms to go outside of the box, yet it still 
>>> happens. Can you give me any tips/ideas on how to do a geometry 
>>> optimizations where atomic positions can only change and the cell geometry 
>>> cannot, or is this not feasible?
>>>
>>> Kind regards,
>>> Lenard
>>>
>>

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