True orthogonality between single-determinant ground state and excited states is achieved through the use of the ab initio local self-consistent-field method. This method allows to optimize the electronic wave function under the constraint of orthogonality to one or several frozen spin-orbitals, virtuals or not. Core- and valence ionization energies of small molecules are computed and show the accuracy of this new scheme. First applications deal with core ionization of macromolecular systems, like proteins or polymers.