About Fix Qeq command

Dear LAMMPS users ,

I have two questions regarding fix qeq command :
1- Can I use this command for small polymers ?

2 - according to manual :

Because the charge equilibration calculation is effectively independent of the pair style, these fixes can also be used to perform a one-time assignment of charges to atoms. For example, you could define the QEq fix, perform a zero-timestep run via the run command without any pair style defined which would set per-atom charges (based on the current atom configuration), then remove the fix via the unfix command before performing further dynamics.

I tried to use this fix but I get some errors like : ERROR: Atom sorting has bin size = 0.0 , that I believe is reasonable !
Do you have any example of using fix qeq without using pair_style?!

Thanks for your attention.
Best ,
Saeed.

Dear LAMMPS users ,

I have two questions regarding fix qeq command :
1- Can I use this command for small polymers ?

​LAMMPS doesn't know or care what kind of material you are simulating. it
is *your* job to feed LAMMPS meaningful parameters and to set up meaningful
models with a proper physical foundation.​

2 - according to manual :

Because the charge equilibration calculation is effectively independent of
the pair style, these fixes can also be used to perform a one-time
assignment of charges to atoms. For example, you could define the QEq fix,
perform a zero-timestep run via the *run*
<http://lammps.sandia.gov/doc/run.html> command without any pair style
defined which would set per-atom charges (based on the current atom
configuration), then remove the fix via the *unfix*
<http://lammps.sandia.gov/doc/unfix.html> command before performing
further dynamics.

I tried to use this fix but I get some errors like : ERROR: Atom sorting
has bin size = 0.0 , that I believe is reasonable !
Do you have any example of using fix qeq without using pair_style?!

​what would be the point of adjusting charges, when you are not using them
for anything?

axel.​

So the purpose of invoking fix qeq without a pair_style defined is to allow charge equilibration without changing the dynamics. After equilibrium charges are obtained, you can use a style and proceed with normal dynamics.

To invoke fix qeq without a style defined, you need to turn off atom sorting. See atom_modify doc page for more info.

Ray