Metal–insulator transition in one-dimensional In-chains on Si(111): combination of a soft shear distortion and a double-band Peierls instability

The most stable geometries for the (4 × 1) and (4 × 2) phases of the In/Si(111) surface have been reanalysed using DFT-annealing. A very efficient local orbital method (FIREBALL) has allowed us to explore the geometrical phase space and look for new absolute minima. The most stable theoretical structure is a new In/Si(111)-(4 × 2) geometry that presents a semiconducting band structure. This (4 × 2) surface, qualitatively very similar to the structural model proposed by Kumpf et al (2000 Phys. Rev. Lett. 85 4916), is found to be the result of the combination of a soft shear distortion, whereby the two zigzag In-rows are displaced in opposite directions along the In-chains, and a pairing of the outer In atoms associated with a double-band Peierls distortion.