Draw the plot of the planar average of ElectrostaticDifferencePotential and see whether the curve at the vacuum region is flat or not.
If the vacuum thickness is too thin, the curve at the center of vacuum region may not flat. In this case, you have to increase the vacuum thickness.
I have added vacuum by changing the lattice parameters and then created a device (simply from bulk to device) and then calculated the ElectronDifferencePotential.
I cannot find much difference, i.e. the curve at the centre of the vacuum region seems to be flat in all the three cases (5A, 10A and 20A vacuum on sides of the width of the ribbon as well as above and below the surface of the ribbon)
C direction is the transport direction where the electrodes are located.
B implies the width of the ribbon.
A is direction perpendicular to the surface.
Could you please tell me how much amount of vacuum must be incorporated for further calculations?
Thanks in advance!