Surface reconstructions and bonding via the electron localization function: the case of Si(001)

The bonding pattern of a covalent semiconductor is disrupted when a surface is cut while keeping a rigid (truncated bulk) geometry. The covalent bonds are partly reformed (with a sizeable energy gain) when reconstruction is a llowed. We show that the "electron localization function" (ELF)-applied wit hin a first-principles pseudopotential framework-provides un unprecedented insight into the bonding mechanisms. In the unreconstructed surface one det ects a partly metallic character, which disappears upon reconstruction. In the surface reformed bonds, the ELF sharply visualizes strongly paired elec trons, similar in character to those of the bulk bonds. (C) 1999 Elsevier S cience Ltd. All rights reserved.