To solve the bound state problem, we require that −V
0<E<0. The relevant boundary conditions are ψ(0)=0, due to the infinitely high barrier at x=0 and limx→∞ψ(x)=0. The solution to the time-independent Schrödinger equation is:
where
Diving these two equations, we obtain,
Note that equation (1) implies that,
We can also rewrite equations (2) and (3) as,
We require
The requirement of k > 0 is conventional, since the sign of k can be absorbed into the definition of the constant A.
Equations (4) and (5) can be solved graphically by looking for intersection of the function
with the circle of radius
in the first quadrant of the xy plane (where x=kb and y=kb ).
It is clear from the figure above that if V
0 is less than some critical value, then the radius of the circle,
in which case there are no intersections in the first quadrant, and therefore no bound states. The critical value of of V
0 is obtained by setting
That is,
which yields,