Discussion Forum

Dear COMSOL Community,

I hope you are doing well. I’m currently working on a 3D simulation of membrane potential using a coupled Poisson–Nernst–Planck (PNP) model in COMSOL Multiphysics 6.3.

I would greatly appreciate any advice or suggestions regarding the issue described below. Thank you in advance for your time and support.

I’m trying to simulate the membrane potential using the following physics interfaces:

• Electrostatics (ES)
• Transport of Diluted Species (TDS)
• Multiphysics coupling: Electromigration in Diluted Species

Two ion species (K⁺ and Cl⁻) are defined with appropriate charge numbers, diffusion coefficients, and initial concentrations inside and outside the cell. The membrane is modeled as a dielectric region (TDS excluded), and the outer solution is modeled as a large domain to approximate a reservoir.

The initial values are set as: - V = 0 V - c_K = 150/5 mol/m³ (inside/outside) - c_Cl = 20/120 mol/m³ (inside/outside)

However, the time-dependent solver fails to converge with the following error message:

"Failed to find consistent initial values.
Last time step is not converged."

Could anyone kindly suggest: 1. How to diagnose inconsistent initial values in this context? 2. Techniques to stabilize the time-dependent solver in a PNP model? 3. Whether a working 3D PNP example involving ion transport through a membrane is available?

Thank you very much for your help!