In the simplest Kronig-Penny model each atom of the solid is represented by a single square well with the same depth. Thus, all atoms in this model of a solid are identical. For most real solids, this assumption does not hold true. A Kronig-Penny model for a solid with more than one element will have square wells with different width and/or depths. A solid which is only slightly more complex than a pure substance has two elements. Most of the atoms are one element with a few being a second impurity element. You will now use the Energy Band Creator to determine the effect on energy levels in a solid with one impurity which is represented by a deeper square well.