Chemisorption bonding, site preference, and chain formation at the K/Si(001)2×1 interface

A variety of possible chemisorption models has been investigated for the K/Si(001)2×1 interface by use of the local-density formalism and the discrete variational method to carry out self-consistent total-energy calculations with Hedin and Lundqvist exchange correlation. Cluster models with up to 89 atoms are adopted to simulate various chemisorption sites. Electronic structures, charge distributions, and bonding characteristics are studied and discussed. The binding energy and relative stability are determined with a total-energy approach. It turns out that the most stable site predicted the cave site has been ignored previously in both theoretical calculations and experimental analyses. However, it is the site towards which dangling bonds of the two nearest surface Si atoms are directed and looks to be a reasonable feature for chemisorption. The resulting K-Si bond length (3.22 A) is in good agreement with the latest surface extended x-ray-absorption fine-structure experimental value. A charge of about 0.5e per K atom is transferred from the K atom to the surface, indicating that a mixed type of bonding occurs. Moreover, for monolayer adsorption, a potassium chain formed on the surface tends to undergo a small zigzag Peierls-like deformation to form a lower-energy state.