The simultaneous ejection of two electrons from non-magnetic surfaces
due to the collision of incident low-energy electrons with valence ele
ctrons is treated in a relativistic distorted-wave Born approximation
including exchange. The primary electron and the two emitted electrons
are described by quasi-particle multiple scattering states. The valen
ce electron is represented by linear combinations of Bloch waves match
ed at the surface. Screened Coulomb interaction matrix elements betwee
n these four states are evaluated. Numerical results for W(0 0 1) are
presented and compared with one-dimensional bulk densities of states.
Energy-integrated spectra and general features of the 2e-distribution
are in good agreement with recent experimental data. (C) 1997 Elsevier
Science Ltd.