Hi everybody, I have participated in a course about solid state physics and have been introduced with Kronig-Penny model. Now in this model, so far I understood we solve the nature of wave function of an electron inside an array of potential barrier. It very nicely explains the concept of conduction band and forbidden band inside solid along with the widths of the bands. Now my question is: in my solid I have lot of electrons (some tightly bonded and some not) and so far I understood, if I had one electron in my system, Kronig penny model describes the energy for that situation like hydrogen atom. So what happens when have many electons inside the system. 1)Should not I have as many as wave equations as electrons and should not they be superimposed on each other , then how the solution should look like? or 2) Do they collectively behave the same way as the single electron so it is not necessary to calculate ? I am not physics major. Hence might be naive in understanding. I would very much appreciate if somebody share their thoughts about it.