The equation of electrodiffusion has the form
|∇ Ji + ∂ni/∂t = 0|
|Ji = - Di(∇ ni + zie ni/(kBT) ∇φi)|
where ni is a number of i – th ions, φ – electric potential, Di – the diffusion coefficient of i – th particles, kB – Boltzmann constant, T – temperature, zi – valence of the i – th kind of ions, e – electric charge. To find the electric potential φ the Poisson equation must be solved
|∇T(ε0ε ∇ φ i) + ρ = 0|
where ρi = zieni. Thus equations (1) and (2) both constitute the system of coupled equations.