Fix typos
Several creative spellings of "Calculating" or "Calculation" appear in the code:
// Caluclating potential at the channel's surface along the x-axis
// Calulating potential for the handover y-position at x_jun, x_ch1 and x_ch2
// Calculaction of the x-position where the TGR is the greatest which is used for the
// Calculaion of the effective built-in volatges at the channel junctions
(also voltages in that last line). Some of the above appear multiple times.
Also: Minimun, Secound, conctants, characteric, densitiy, libraray.