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Abstract:
A sum rule for ionization potentials, similar to the Manne-Åberg theorem, is derived in the framework of a many-body Green's-function formalism. This sum rule is shown to be valid under mainly two conditions: (i) the constant term and the affinity poles of the self-energy part have to be neglected; (ii) the final state wavefunction has to be separable in a free-electron and an (N - 1)-electron part. The latter assumption is discussed in connection with the sudden approximation which is not used for the derivation of the new sum rule.
