electron and proton in electric field

Are you trying to simulate a system like laser + plasma interaction?

Well, easiest way to model electron + ion plasma with immobile ions is –

  1. Create electrons and ions both in your system and make ions artificially too heavy.
  2. Avoid any Coulomb collapse by choosing pseudo potentials

Or, if you are interested in only electron dynamics, try to model only electron plasma (keeping in mind uniform neutralizing background).

Hope it helps!