  The one-step model of valence-band photoemission and inverse photoemission
from single-crystal surfaces is reformulated for generalized (non-local,
complex and energy-dependent) potentials. Thereby, it becomes possible to
account for self-energy corrections taken from many-body electronic-structure
calculations. The original formulation due to Pendry and co-workers employs the
KKR multiple-scattering theory for the calculation of the initial state. This
prevents a straightforward generalization of the one-step model to non-local
potentials. We therefore consider the Dyson equation which is set up within a
muffin-tin-orbitals representation as an alternative to obtain the
initial-state Green function. This approach requires a revision of the
transition-matrix elements which is carried out in detail. The final state is
considered as a time-reversed LEED state as usual. The proposed generalization
of the one-step model allows to distinguish between the bare photocurrent
reflecting the (quasi-particle) band structure and the secondary effects due to
the (dipole) selection rules and due to the wave-vector and energy dependence
of the transition-matrix elements.
