# How to understand the energy derivative of the logarithmic derivative of a wavefunction when deriving norm-conserving pseudopotentials

The 4th desirable property of a norm-conserving pseudopotential given by Hamann et al is for the 'logarithmic derivatives of the real and pseudo wave function and their first energy derivatives agree for $$r>r_c$$'. However I do not understand how the energy derivative of the log derivative $$\frac{d}{d\epsilon}r\frac{d}{dr}\ln\psi(\epsilon;r)$$ can be defined. In the all-electron case, my understanding is that the valence states are discretised (traditionally labelled with $$(n,l,m)$$). So what are the states $$\psi(\epsilon;r)$$ with continuous $$\epsilon$$ that are presumably required to allow us to define the energy derivative of the log derivative above?

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