The Space charge density boundary condition fixes the space charge density to a specific value.

Select an option from the Specify space charge density using list — Space charge density (the default) or Number density.

When Space charge density is selected enter a value or expression for the Space charge density ρ0 (SI unit: C/m3). When Number density is selected enter a value or expression for the Number density n0 (SI unit: 1/m3). The actual space charge density is then computed by multiplying the number density by the elementary charge.