A didactically motivated reexamination of a particle’s quantum mechanics with square-well potentials

We address two questions regarding square-well potentials from a didactic perspective. The first question concerns whether or not the justification of the standard a priori omission of the potential’s vertical segments in the analysis of the eigenvalue problem is licit. The detour we follow to find out the answer considers a trapezoidal potential, includes the solution, analytical and numerical, of the corresponding eigenvalue problem and then analyzes the behavior of that solution in the limit when the slope of the trapezoidal potential’s ramps becomes vertical. The second question, obviously linked to the first one, pertains whether or not eigenfunction’s and its first derivative’s continuity at the potential’s jump points is justified as a priori assumption to kick-off the solution process, as it is standardly accepted in textbook approaches to the potential’s eigenvalue problem. We show that, by following the indicated detour, the irrelevance of the potential’s vertical segments and the continuity of eigenfunctions and their first derivatives at the potential’s jump points turn out to be proven results instead of initial assumptions.

Keywords:
Quantum mechanics; square-well potentials