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Homework Help: Van der Waals Potential

  1. Apr 9, 2009 #1
    1. The problem statement, all variables and given/known data
    The van der Waals potential between two inert atoms is often characterized by the expression:

    http://bama.ua.edu/~stjones/253hw_files/image025.gif [Broken]

    Sketch the function. Expand the potential around the minimum in the form U = U(ro) + ½ k(r-ro)2. Evaluate k in terms of s and e.

    2. Relevant equations

    3. The attempt at a solution
    I got the sketch down fine. I am just unclear about the second part. Nothing in my physics textbook helps. What i have done so far is take the original equation and substitute it in
    U = U(ro) + ½ k(r-ro)2. Doing that i got:

    U = 4e[(σ/ro)^12-(σ/ro)^6] + ½ k(r-ro)2

    From there i solved for k and got:


    Im not sure if im the right path but from here i dont know how to get k in terms of s and e. Any help is greatly appreciated!
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 9, 2009 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Are you familiar with Taylor Series expansions (from when you took calculus)? That's the key to solving this one.
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