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

[fa...@gmail.com]

&fixed_atoms does not fix the cartesian but the fractional coordinates. In 
a geo_top, nvt, nvt this is the same, but if you perform a cell_opt or npt 
the cartesian coordinate of atoms can still change.

Best,
Fabian

On Thursday, 6 August 2020 at 13:08:19 UTC+2 ka... at gmail.com wrote:

> Dear Matt
>
> First of all, I'm sorry.
> Now I noticed that coordination is wrong.
> I mean "coordinates".
>
>
>
> Do you mean &fixed_atoms and cell parameters are independent?
>
> Well, in my case, xyz lengths of the cell and the distances among atoms 
> are the same, because all fixed atoms form the cell frame(a cube shape).
> I have already checked and confirmed that they are the same length.
>
> The coordinates should have been fixed with &fixed_atoms, according to 
> manual.
> Nevertheless coordinates of atoms were changed at the output.
>
> I don't understand this.
>
>
> 2020년 8월 6일 목요일 오후 6시 51분 6초 UTC+9, Matt W 님의 말:
>
>> 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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