  Absorption of Pt on the Ge(001) surface results in stable self-organized Pt
nanowires, extending over some hundred nanometers. Based on band structure
calculations within density functional theory and the generalized gradient
approximation, the structural relaxation of the Ge--Pt surface is investigated.
The surface reconstruction pattern obtained agrees well with findings from
scanning tunneling microscopy. In particular, strong Pt--Pt dimerization is
characteristical for the nanowires. The surface electronic structure is
significantly perturbed due to Ge--Pt interaction, which induces remarkable
shifts of Ge states towards the Fermi energy. As a consequence, the topmost Ge
layers are subject to a metal-insulator transition.
