[CP2K-user] The cutoff unit in CP2K

[msha...@gmail.com]

Dear Marcella, Thank you very much again for your response.

On Saturday, January 16, 2021 at 1:06:17 PM UTC+3:30 Marcella Iannuzzi 
wrote:

> Coarser grids are used to collocate contributions to the density from 
> smoother functions. 
> The total density is then obtained on the finest grids using interpolation 
> operators.
> This operation can lead to differences depending on the choice of the 
> grids. 
> Please find more details in 
> VandeVondele, J.; Krack, M.; Mohamed, F.; Parrinello, M.; Chassaing, T.; 
> Hutter, J. Quickstep: Fast and Accurate Density Functional Calculations 
> Using a Mixed Gaussian and Plane Waves Approach. *Comput Phys Commun* 
> *2005*, *167* (2), 103–128. https://doi.org/10.1016/j.cpc.2004.12.014.
>
> Regards
> Marcella
>
> On Saturday, January 16, 2021 at 10:06:42 AM UTC+1 msha... at gmail.com 
> wrote:
>
>> Dear Marcella,
>>
>> Thank you very much for your response. I have another question about 
>> this, what is the effect of NGRIDS keyword on the calculations. I see 
>> increasing the NGRIDS increase the speed of calculations but there are 
>> small differences in the total energy calculations. How does NGRIDS affect 
>> the calculations?
>>
>> Thank you so much again.
>> On Saturday, January 16, 2021 at 12:29:29 PM UTC+3:30 Marcella Iannuzzi 
>> wrote:
>>
>>>
>>> In GPW the electron density, and not the wave functions, is expanded in 
>>> PW.
>>> Therefore the PW cutoff is four time as large as a the one you would use 
>>> to expand the wave functions, as it is done in Quantum ESPRESSO.
>>> Whether or not the grids and PW parts of one GPW calculation become 
>>> expensive and dominant depends on the system and on the method you are 
>>> using. Hence increasing the PW cutoff, within a reasonable range, is often 
>>> not too problematic.
>>> Regards
>>> Marcella
>>>
>>> On Saturday, January 16, 2021 at 8:46:10 AM UTC+1 
>>> msha... at gmail.com wrote:
>>>
>>>> Hello everyone,
>>>>
>>>> I wanted to ask a question about the cutoff value unit. The unit in the 
>>>> manual is in Ry and the default value is 280 Ry and for some systems, we 
>>>> may need to increase this value. I wanted to know why would we need such 
>>>> huge values? In Quantum ESPRESSO 60-80 Ry is fine for some calculations and 
>>>> adopting higher values is computationally expensive. Can you please explain 
>>>> a bit more about the unit of the cutoff in CP2K? and why in CP2K a larger 
>>>> value is required than QE?
>>>>
>>>> Thank you very much in advance.
>>>>
>>>
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