Electrical model for graphene in DEVICE



I have a question regarding the KB example of electrical modeling for graphene in DEVICE
I need to understand how was the electron density extracted from a 3D device simulation as shown in the figure below? Is the change in the chemical potential due to applied voltage?? In other words, what is the simulation setup of which you can get those results?


The independent variable in this plot is the electron density. In order to create this plot, we applied a uniform n-type doping on a 0.1 nm thick graphene sheet. The doping value was varied using a parameter sweep and the corresponding chemical potential was calculated using a bandstructure monitor (chemical potential = Efn - Ei). No bias voltage was applied (the sheet was kept grounded) rather the shift in chemical potential was achieved through doping.
One point to note here is that the doping object takes a 3D electron (dopant) density as input (/m^3). The corresponding 2D electron density (x-axis of the plot) can be found by multiplying the 3D density with the thickness of the graphene sheet (here, 0.1e-9 m). For example, a constant doping of 2.5e22 /cm^3 (or 2.5e28 /m^3) will result in a 2D electron density of 2.5e28*0.1e-9 = 2.5e18/m^2.