[CP2K-user] how to choose the size of the cell correctly?

[Malin Khalil]

Thank you all for the answers!

في الاثنين، 1 فبراير 2021 في تمام الساعة 1:45:44 ص UTC+3، كتب Travis رسالة 
نصها:

> Hi,
>
> Switch to non-periodic boundaries (PERIODIC NONE in both &CELL and 
> &POISSON sections, use the WAVELET solver in &POISSON, and add 
>
> &CENTER_COORDINATES
> &END CENTER_COORDINATES
>
> to &TOPOLOGY section. The molecule will be default centered at L/2 where L 
> is the box length in a given direction. Add a 6 Angstrom buffer in your 
> &CELL section between the molecule and the box edge on each side: top, 
> bottom, left, right, front, back. If you need to increase the buffer 
> distance, you'll see a warning printed at each SCF iteration that says the 
> electron density isn't close enough to zero at the box edge. Just increase 
> your buffer in 1 Angstrom increments until the error no longer shows up. 
> You don't want to immediately set the box size to be very large as the 
> vacuum is filled with plane waves and so adds considerable computational 
> expense. You can have different size a, b, and c lattice vectors for such a 
> calculation.
>
> -T
>
> On Saturday, January 30, 2021 at 5:44:03 PM UTC-5 mal... at gmail.com 
> wrote:
>
>> Hello everyone!
>>  I'm trying to calculate homo lumo gap of single walled carbon nanotubes, 
>> for the &SUBSYS &CELL I'm choosing the ABC as following: add 2 angstroms to 
>> the longest distance in each dimension. Am I doing everything right?
>> I attached my input file and the structure of the CNT (9,0) which i'm 
>> studying now.
>> best regards,
>> Malin 
>>
>
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