Kronig-Penney model of a 1-D periodic potential and resulting dispersion and density-of-states curves

Program to plot the dispersion curve and density of states of a 1-D array of atoms according to the Kronig-Penney model, a simplified model in solid-state physics for electrons in a one-dimensional pulselike periodic potential. See for example https://en.wikipedia.org/wiki/Particle_in_a_one-dimensional_lattice for the physics background.

The program allows the user to vary one of three parameters - the height of the rectangular potential representing the ionic cores; the periodicity of the 1-D array; and the duty cycle of the array, i.e., the ratio of the width of the rectangular pulse to the periodicity. Three examples are provided.