I would like to set up two dielectric constant.
I am simulating cylindrical dna in the presence of positive and negative ions.
Dielectric constant of DNA is much lower than that of water.
I want to set up dieletric constant to 2 inside cylindrical DNA,
and set up dielectric constant to 78 outside DNA in water.
Then, I don't know how to set up two dielectric constants,
and I don't know either how to set up pair-style and pair coefficient.
I am using lj/cut/coul/cut now.
I appreciate any comments from Lammps fellows.
Dielectric properties are emergent properties of the system, ie. if your molecular modelling is right, you should get the right dielectric constant. Some water models (eg SPC/E) get it pretty close, for DNA I have no idea.
Your model is unclear to me. If you want one
equation (with one constant) to be calculated for
some pair interactions, and a different eq for
others, you could write (or derive) a pair potential
to do that. But for a charged system, you probably
also have a long-range component, for which it
doesn't make sense to have 2 dielectric constants.