Zigzag equilibrium structure in monatomic wires
  We have applied first-principles density-functional calculations to the study of the energetics, and the elastic and electronic properties of monatomic wires of Au, Cu, K, and Ca in linear and a planar-zigzag geometries.   For Cu and Au wires, the zigzag distortion is favorable even when the linear wire is stretched, but this is not observed for K and Ca wires.   In all the cases, the equilibrium structure is an equilateral zigzag (bond angle of 60$^{\rm o}$).   Only in the case of Au, the zigzag geometry can also be stabilized for an intermediate bond angle of 131$^{\rm o}$.   The relationship between the bond and wire lengths is qualitatively different for the metallic (Au, Cu and, K) and semiconducting (Ca) wires. 
Daniel Sanchez-Portal, Emilio Artacho, Javier Junquera, Alberto   Garcia, and Jose M. Soler