The Surface Charge Density node provides the following surface-charge boundary condition for exterior boundaries (left) and interior boundaries (right):

Specify the surface charge density ρs at an outer boundary or at an interior boundary between two nonconducting media.

Add a contribution as a Harmonic Perturbation by right-clicking the parent node or click Harmonic Perturbation on the Physics toolbar. For more information, see Harmonic Perturbation — Exclusive and Contributing Nodes in the COMSOL Multiphysics Reference Manual.

Enter the value or expression for the Surface charge density ρs (SI unit: C/m2).