How to find the wave function using WKB?

In summary, the conversation discusses finding wave functions using the WKB method for an electron in a nuclear potential. Specifically, for the given potential and barrier region, the wave function inside the barrier region is given by the equation provided. The conversation also mentions performing an integral, but it is not clear if it is necessary for finding the wave function.
  • #1
a1111
2
0
I would like to understand how to find wave functions using WKB.

Homework Statement



Given an electron, say, in the nuclear potential

$$U(r)=\begin{cases}
& -U_{0} \;\;\;\;\;\;\text{ if } r < r_{0} \\
& k/r \;\;\;\;\;\;\;\;\text{ if } r > r_{0}
\end{cases}$$

With the barrier region given by:

$$r_{0} < r < k/E$$

What is the wave function inside the barrier region?

Homework Equations



See below.

The Attempt at a Solution



For E > U(r):

$$\psi(r)=\frac{Ae^{i\phi(x)}}{\sqrt{2m(E-U(r)}}+\frac{Be^{-\phi(x)}}{\sqrt{2m(E-U(r)}}$$

$$\phi(r)=\frac{1}{\hbar}\int^{r}_{0}\sqrt{2m(E-U(r')}=\frac{1}{\hbar}\int^{r}_{0}\sqrt{2m(E+U_{0})}dr'=\frac{r\sqrt{2m(E+U_{0})}}{\hbar}$$

Is the above integral correct? Is that simply all that I needed to do?
 
Last edited:
Physics news on Phys.org
  • #2
For the barrier region, what is the wave function inside it?The wave function inside the barrier region is given by:$$\psi(r)=Ae^{ikr/\hbar}+Be^{-ikr/\hbar}$$
 

Related to How to find the wave function using WKB?

1. What is the WKB method and how does it relate to finding the wave function?

The WKB (Wentzel-Kramers-Brillouin) method is a semi-classical approximation technique used to solve the Schrödinger equation in quantum mechanics. It is based on the idea of treating the wave function as a slowly varying quantity and using this information to approximate the solution.

2. What are the assumptions made in the WKB method?

The WKB method makes two main assumptions: first, that the potential energy is slowly varying, and second, that the wavelength of the wave function is much smaller than the characteristic length scale of the potential. These assumptions allow for a simplified solution to the Schrödinger equation.

3. How do you apply the WKB method to find the wave function?

To apply the WKB method, you first need to solve the classical equation of motion for the system. Then, you use this solution to construct an approximate form for the wave function, which is given by a product of an amplitude and a phase term. Finally, you match this approximate form to the exact solution of the Schrödinger equation at certain points to determine the coefficients in the amplitude and phase terms.

4. What are the limitations of the WKB method?

The WKB method is only accurate for certain types of potentials and may fail for highly oscillatory or rapidly changing potentials. It also does not account for quantum phenomena such as tunneling and interference, so it is not suitable for all systems in quantum mechanics.

5. Can the WKB method be extended to higher dimensions?

Yes, the WKB method can be extended to higher dimensions, but it becomes more complicated and less accurate. In higher dimensions, the wave function is a function of multiple variables, making it more difficult to approximate. Other methods such as perturbation theory may be more useful in these cases.

Similar threads

  • Advanced Physics Homework Help
Replies
29
Views
351
  • Advanced Physics Homework Help
Replies
30
Views
2K
  • Advanced Physics Homework Help
Replies
4
Views
992
  • Advanced Physics Homework Help
Replies
14
Views
1K
  • Advanced Physics Homework Help
Replies
1
Views
1K
  • Advanced Physics Homework Help
Replies
1
Views
1K
  • Advanced Physics Homework Help
Replies
3
Views
2K
  • Advanced Physics Homework Help
Replies
3
Views
1K
  • Advanced Physics Homework Help
Replies
4
Views
1K
  • Advanced Physics Homework Help
Replies
2
Views
1K
Back
Top