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

[Matt W]

To my knowledge it fixes the cartesian position of the atoms listed. The 
cell parameters are free to adjust if you perform a cell optimization.

Matt

On Wednesday, August 5, 2020 at 11:49:06 AM UTC+1 ka... at gmail.com wrote:

> Hello, everyone
>
>
> I try to optimize cell coordinate with &fixed_atoms.
> I thought that it will be optimized not to change coordination because of 
> the word "fix"
> and I read the manual says that "specifies a list of atoms to freeze".
>
> But I noticed that the coordination is changed somewhat at the output file.
> What is the principle of the &fixed_atoms?
> Doesn't it just freeze or fix the coordination?
>
> This is a part of my input.
> &MOTION
>   &CELL_OPT
>     KEEP_ANGLES .T.
>   &END CELL_OPT
>    &CONSTRAINT
>      &FIXED_ATOMS
>         LIST 1..56
>      &END FIXED_ATOMS
>    &END CONSTRAINT
> ...(omission)...
>
>   &SUBSYS
>     &CELL
>       ABC              10.166 10.166 10.166
>       ALPHA_BETA_GAMMA 90.0   90.0   90.0
>       PERIODIC  XYZ
>       MULTIPLE_UNIT_CELL  1 1 1
>     &END CELL
> ...(omission)...
>
> And, at the output file, the cell vector ABC was changed to 10.436 at the 
> Fe2+ lattice, to 10.447 at the Zn2+ lattice and so on.
>
> If anyone understands about this, please tell me.
>
>
> Thanks for your attention.
>
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