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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def collective_diffusion_coefficient( self ):
 """ Returns the collective or "jump" diffusion coefficient, D_J. Args: None Returns: (Float):
 The collective diffusion coefficient, D_J. """

        if self.has_run:
            return self.atoms.collective_dr_squared() / ( 6.0 * self.lattice.time )
        else:
            return None