calculating box length in charged system part2

[Ahmad Reza Motezakker]

Dear All, 

I was going through the tutorial for the charged system Part 2 and I did not understand why in calculation of box length in x and y direction, we take into account all the masses including electrode mass as follows:

(box_l = (n_ionpairs * sum(masses.values()) / density)**(1. / 3.))

which masses is : masses      = {"Cl":  35.453, "Na": 22.99, "Electrode": 12.01}

​I really appreciate your help

Best Regards,

Ahmad Reza