How to fix and unfix an atom?

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#1

Hellow lammps users,

I want to fix an atom during some time setups, and then unfix it.

fix

velocity pointfixed set 0.0 0.0 0.0
fix 1 pointfixed setforce 0.0 0.0 0.0

run 10000

unfix

velocity pointfixed set NULL NULL NULL

unfix 1

run 10000

The fix part works but unfix part can’t work, so would you have other solutions for fixing and unfixing an atom?

Meng LIAO

#2

Hellow lammps users,

I want to fix an atom during some time setups, and then unfix it.

## fix

velocity pointfixed set 0.0 0.0 0.0
fix 1 pointfixed setforce 0.0 0.0 0.0

run 10000

## unfix

velocity pointfixed set NULL NULL NULL

unfix 1

run 10000

The fix part works but unfix part can't work, so would you have other
solutions for fixing and unfixing an atom?

​the unfix *definitely* works. however, your second velocity command makes
no sense, as it doesn't do anything.​
there is not enough information there to explain why you don't get what you
expect.

axel.

#3

I also want to unlock the atom’s velocity, how can I set the atom free?

Re: [lammps-users] How to fix and unfix an atom?

#4

I also want to unlock the atom's velocity, how can I set the atom free?

​you have erased it. it is gone.​ you have to assign a new velocity.

axel.

#5

… or follow a different strategy to immobilize your atom: do not include it in time integration.
this way, it will retain its velocity, you compute its forces, but don’t update either position or velocity.

axel.

#6

I also want to unlock the atom's velocity, how can I set the atom free?

​you have erased it. it is gone.​ you have to assign a new velocity.

axel.

You could also try the fix martin/luther/king command ...

Steve

#7

I also want to unlock the atom’s velocity, how can I set the atom free?

You could also try the fix martin/luther/king command …

Really, just silence from the mail list? This was my best joke in months …

Steve

#8

>> I also want to unlock the atom's velocity, how can I set the atom free?

> You could also try the fix martin/luther/king command ...

Really, just silence from the mail list? This was my best joke in months
...

​it is *too* good. how can one top this?

axel.