  The authors introduce a geometry for ultrathin Au and Ag wires that ab initio
calculations indicate to be more stable than previously considered planar
geometries for these systems, by about 0.1 eV per atom. This structure is
insulating for both metals and for related Ag_(0.5)-Au_(0.5) alloys, with gaps
of 1.3 eV for Au, 0.8 eV for Ag, and varying between 0.1 eV and 1.9 eV for the
alloys. The insulating nature of the geometry is not a result of Peierls
instabilities, and is analyzed in terms of an interplay between geometric and
electronic structure effects.
