The response part originates from the functional derivative of the ε xc factor in the total energy. Given DFAs with good total energies, the error in the orbital energies should not come from the hole part of the exchangecorrelation potential -indeed, it has been argued that the error is in the response potential. It is quite common that an approximation to an integrand is decent in the sense that the integral (the energy) is well approximated, while the derivative of the integrand (the potential) is still very poor.