  An improved formulation of the one-step model of photoemission from crystal
surfaces is proposed which overcomes different limitations of the original
theory. Considering the results of an electronic-structure calculation, the
electronic (one-particle) potential and the (many-body) self-energy, as given
quantities, we derive explicit expressions for the dipole transition-matrix
elements. The theory is formulated within a spin-polarized, relativistic
framework for general nonspherical and space-filling one-particle potentials
and general nonlocal, complex and energy-dependent self-energies. It applies to
semi-infinite lattices with perfect lateral translational invariance and
arbitrary number of atoms per unit cell.
