Direct-space analysis of the Si–Si bonding pattern in the π-bonded chain reconstructed Si(111)(2 × 1) surface

Abstract.

Atomic and bond properties of silicon atoms in the buckled π-bonded chain reconstructed Si(111)(2 × 1) system were investigated by applying the quantum theory of atoms in molecules to a number of wavefunctions from periodic ab initio calculations 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 topmost chain (from the “up” to the “down” atom) was found to be opposite to what was claimed previously. The π conjugation is not strictly localized along the topmost layer chains (where it is also largely incomplete), but rather it extends over a 2D array of bonds between the topmost and the lower surface layers.