[CP2K-user] What is the principle of &fixed_atoms?

fa...@gmail.com fabia... at gmail.com
Fri Aug 7 07:30:08 UTC 2020

The fractional coordinates describe the position with respect to the cell 
dimension while the cartesian ones reference with respect to the the origin 
(0,0,0). Therefore, changing the cell dimension (CELL_OPT) you modify the 
reference for the fractional coordiates but not for the cartesian ones.

Let me give you a simple example:

Assume we have a 1D system, with a cell from 0 to L and one atom in the 
middle. The fractional coordinate of the atom is 0.5, the cartesian one  
Now you fix the fractional coordinate of the atom (such that the atom 
remains exactly in the middle of the cell) and change the cell length to 
2*L. The new cartesian coordinate is now (2*L)/2=L even though the atom was 


On Friday, 7 August 2020 at 06:42:49 UTC+2 ka... at gmail.com wrote:

> I actually understood hardly but I think I got some hints thanks to you 
> all.
> If anyone wants to supplement the explanation, please write here.
> Again, thank you everyone.
> 2020년 8월 6일 목요일 오후 10시 49분 4초 UTC+9, Travis 님의 말:
>> Hi,
>> Fractional coordinates are converted back to Cartesian by multiplying by 
>> the lattice lengths and shape (if not 90 degrees). Cartesian coordinates 
>> can then change if the box size changes.
>> Through freezing or thawing atom positions, fixing angles, or fixing 
>> symmetry you can perform pretty much all the same calculations as listed on 
>> the VASP wiki for the isif keyword (has an easy to read table).
>> -T
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