# Overlap in highly charged particles

Hi dear users
Im simulating a large highly charged particle which attracts other particles (which are smaller with lower charge), but there is a problem:
I obtained xyz dump of atoms and I discovered that attracted atoms are highly overlapped with large particle, so that the distance of these atoms with the center of large particle is less than radius of the particle. It seems that the coulomb potential becomes very powerful and it overcomes to LJ potential in some distances.
So can this matter occur in real physics?
if no how can I remove this problem?
thanks alot
Ly

That's not a physics question, it's a model question.
You are setting the strength of the Coulomb attraction
and the LJ repulsion. So it's up to you to balance
those 2 forces appropriately.

Steve

Hi dear users
Im simulating a large highly charged particle which attracts other particles
(which are smaller with lower charge), but there is a problem:
I obtained xyz dump of atoms and I discovered that attracted atoms are
highly overlapped with large particle, so that the distance of these atoms
with the center of large particle is less than radius of the particle. It
seems that the coulomb potential becomes very powerful and it overcomes to
LJ potential in some distances.

i don't understand why this surprises you.
the coulomb potential is q_i * q_j / (r_ij) so
even if one of the charges is small(er), the
other will overcompensate for it, if it is very
large. what matters is the product.

So can this matter occur in real physics?
if no how can I remove this problem?

this is the wrong way to look at the problem.
your first question should be: what does happen
in real life? and then the second one would be:
what is a good model for it?

designing a model without consideration for
what it should represent, is "problematic".

axel.

Now if I want to consider a hard particle with the same hardness for different charges, what is your idea?
I think I can do it with definition of shift potential besides an offset radius for LJ potential:
4ε((σ/r-roffset)^12-(σ/r-roffset)^6)+Vshift r-roffset<rcut
So can I define this potential in lammps?
And is there any other way to achieve this goal?
Thanks alot
Ly

You can look at pair lj/expand or tabulate your own
pair interaction with pair table.

Steve

Now if I want to consider a hard particle with the same hardness for
different charges, what is your idea?

"hard" particles are what the granular models offer.
but let me rephrase, before obsessing about implementing
something that you expect to see, you should first discuss
what it is that you want to model. i suspect that your
expectations for the model could be wrong and thus
desperately trying to make the simulation look like you
want it to look like may only get you farther away from
doing a meaningful simulation.

doing physics and not computer animations.

I think I can do it with definition of shift potential besides an offset