Figure 1
(a) Top and side views of the optimized c(4 × 2) structure of Si(001). The c(4 × 2) unit cell is indicated by the dashed line. The x (y) axis is perpendicular (parallel) to dimer rows, while the z axis is along the [001] direction. For distinction, the Si-dimer atoms within and outside the c(4 × 2) unit cell are drawn with two different dark circles. In (b), the symmetric double-well potential for the flipping of buckled dimers is schematically drawn. Here, Eb denotes the energy barrier, obtained by the energy difference between the p(2 × 1) and c(4 × 2) structures.
