Direct-space analysis of the Si-Si bonding pattern in the pi-bonded chain reconstructed Si(111)(2x1) surface

Atomic and bond properties of silicon atoms in the buckled pi-bonded chain reconstructed Si(111)(2x1) system were investigated, by applying the Quantum Theory of Atoms in Molecules to a number of wavefunctions from periodic ab-initio calculations, obtained using a slab model for the surface and geometries from experiment. Reconstruction involves much larger surface-cell charge distortions than in the unrelaxed surface and drastic changes in the atomic polarizations of the surface layer atoms. The effect of buckling is to largely differentiate the properties (charge, energy, volume, atomic polarizations) of the two unique atoms of each surface layer. The direction of electronic charge transfer in the top-most chain (from the "up" to the "down" atom) was found opposite to what claimed previously. The pi-conjugation is not strictly localized along the top-most layer chains (where is also largely incomplete), but it rather extends over a two-dimensional array of bonds between the top-most and the lower surface layers.