[lammps-users] Help regarding poly electrolyte modeling for good solvent and poor solvent conditions

Hi

I am Sierra, I am an independent researcher trying to work with LAMMPS. I am trying to model polyelectrolyte for good and bad solvent conditions. It seems that the good solvent condition is working fine for me but when I am trying to model the bad solvent the polyelectrolyte tends to form aggregates and form a globule. What can be the possible solution for this?
I have attached the pair coefficients here for bad solvent.
group polymer type 1 2
group cion type 3
group charged 1 3
pair_style lj/cut/coul/long 2.5 7.5
pair_modify shift yes

pair_coeff 1 1 1.0 1.0 2.5
pair_coeff 1 2 1.0 1.0 2.5
pair_coeff 1 3 1.0 1.0 1.12246
pair_coeff 2 2 1.0 1.0 2.5
pair_coeff 2 3 1.0 1.0 1.12246
pair_coeff 3 3 1.0 1.0 1.12246

I have attached the pair coefficient for the good solvent conditions:
group polymer type 1 2
group cion type 3
group charged 1 3
pair_style lj/cut/coul/long 1.12246 7.5
pair_modify shift yes
pair_coeff 1 1 1.0 1.0 1.12246
pair_coeff 1 2 1.0 1.0 1.12246
pair_coeff 1 3 1.0 1.0 1.12246
pair_coeff 2 2 1.0 1.0 1.12246
pair_coeff 2 3 1.0 1.0 1.12246
pair_coeff 3 3 1.0 1.0 1.12246

Regards
Sierra C

two comments on this:

  • first, this is not really a question about LAMMPS but about your research. so this is not a good place to ask questions. you need to find a place where people discuss their research or - even better - find a more experienced collaborator that you can discuss your work with
  • second, you chance interactions from being entirely repulsive to to being in part attractive, so what you observe is what you should expect, i.e. that the attractive parts try to come together. and that matches the behavior you would expect from a “bad” solvent. so you get out of your simulation what you put in. why does it need a solution? in general, a simulation can only be as good as the model you simulate. your approach to ask for a solution to make a simulation do what you expect is turning research upside down. instead you need to try to understand why a model does what it does, and how you need to construct a model that is more representative of what you want to represent, if that is in fact meaningful. or need to realize that your expectations were not accurate.