EQUILIBRIUM STRUCTURE OF THE INP(100) SURFACE

We use ab initio total-energy minimization methods to study the equilibrium structure of the InP(100) surface, and in particular examine the structure of the surface as a function of In coverage (Theta). We find the low-coverage (Theta = 0.25), non-dimerized (2 x 4) surface to yield the lowest energy per In atom, and therefore to possibly constitute the ground-state structure of the surface, even though it has not been observed experimentally. Nevertheless, we have found the In-dimerized surfaces at all. coverages to be stable. For the fully In-covered surface, we observe the equilibrium structure to be the symmetric (2 X 1) phase, i.e., with the In dimers adopting a symmetric configuration with respect to the surface. For a coverage of Theta = 0.75, we find a symmetric-dimer (2 X 4) reconstruction to provide a stable equilibrium configuration. The dimer bond length, we observe, is relatively insensitive to coverage, and in view of the fact that LDA calculations tend to underestimate distances a little, we predict that the experimental bond-length value should be very dose to 2.8 Angstrom. For low In coverage surface, our calculations indicate that phosphorus dimers may form.