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Double Delta function potential well

  1. Apr 2, 2013 #1
    Consider a one-dimensional system described by a particle of mass m in the presence
    of a pair of delta function wells of strength Wo > 0 located at x = L, i.e.
    V(x) = -Wo (x + L) - Wo(x - L) This is a rough but illuminating toy model of an electron in the presence of two positive.
    charges located at x = L.

    (a) Derive a transcendental equation for the allowed eigenenergies of any bound states.
    Express your result in terms of the dimensionless quantities go = mLWo/hbar^2 and ε = κL where E = -hbar^2*κ^2 / 2m is the (negative) energy of the bound state.

    (b) Solve your transcendental equation(s) graphically / numerically to identify all
    bound state energy eigenvalues. How many bound states exist? Does the number
    depend on go?

    (c) Plot all bound state energy eigenfunctions for go = 0.1, go = 0.5 and go = 10.

    (d) How does the energy of the most tightly bound state vary as you vary L? Include
    a plot (with axes and units labeled) which shows the energy as a function of L.
    Note: You do not have to do this analytically; this is most easily done numerically
    using Mathematica.

    (e) Suppose we place the particle in the lowest energy bound state. Do the two delta
    functions want to be close together or far apart? Plot the induced force between
    the delta functions as a function of L. Again, best done numerically.

    (f) Use the above to suggest a plausible explanation for why H+2
    is a stable molecule.

    (g) How does the splitting between levels change as you increase the separation between the wells? Why does the 2rd excited state have the same number of nodes inside each well as the 3rd excited state, but not the same number as the 4th?

    So I think I did a). I got ε = go(1-e^(-2ε)) and ε = go(1+e^(-2ε)). I'm not suite sure what b) is. I thought it was 2. The thing I'm getting hung up on c) -g) bc I can't use mathematica to its full 'potential' I guess. Help please? How do I proceed.
  2. jcsd
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