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Homework Help: Koopmans theorem

  1. Apr 30, 2008 #1
    Hi all,

    I am using Koopmans theorem trying to estimate excitation energy so I have calculated the homo/lumo for molecule A as well as for A- and A+(adding and removing an electron respectively). Then I would use the formula

    Egap = min[(E(n+1)-E(n)]-[E(n)-E(n-1)]]

    I get a energy gap which is smaller than the experimental value(1 eV less) does this seem like a reasonable computation?

    Any advise appreciated - thanks in advance

  2. jcsd
  3. May 1, 2008 #2


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    Is this gas phase or solid phase?
  4. May 1, 2008 #3
    it is in gas phase
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