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Van del waals interaction in qm

  1. Nov 5, 2013 #1

    I read the follow paper about van del waals interaction in quantum mechanics


    In this paper the potential

    [tex]V= e^2/R + e^2/(R+y)+e^2/(R-x)+ e^2/(R+y-x) [/tex]

    is aproximated to [tex]V \approx -2 e^2/R^3 xy[/tex]

    with R>>|x|,|y|

    why this paper use this aproximation?

    if i use Taylor series, my aproximation is

    [tex]V=4 e^2 /R + 2 e^2/R (x-y) + 2 e^2 /R^3 (x^2+y^2) -2 e^2/R^3 xy[/tex]
  2. jcsd
  3. Nov 5, 2013 #2
    ohh, sorry, my problem is with signus of V....delete my post please
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