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Wave eqtion of electron in a periodic potential

  1. Feb 8, 2010 #1
    quoted from Kittel text 8th edition page 170,171
    the potential energy is U(x)=[tex]\Sigma[/tex][tex]U_{G}e^{iGx}[/tex]

    but why it is also equal to-> U(x)=[tex]\Sigma[/tex][tex]U_{G}e^{iGx}+e^{-iGx}[/tex]

    from text explanation, i couldn't get it why there is an extra term of [tex]e^{iGx}[/tex]

    any 1 care to enlight me on this? thanks.
  2. jcsd
  3. Feb 14, 2010 #2
    There is an extra term e-iGx to make potential energy U(x) a real function.
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