Atomic and electronic structure of ideal and reconstructed alpha-Sn (100) surfaces

alpha-Sn(100) surfaces have been recently produced through epitaxial growth of Sn on ZnSb (100). Reflection high-energy electron-diffraction data on t hese surfaces exhibit a variety of reconstructions with periodicities 2 x 1 , p(2 x 2), and c(4 x 4), attributed to possible ordering of dimers, in ana logy to Si(100) and Ce(100) surfaces. Here we present a theoretical study o f alpha-Sn(100) using the ab initio pseudopotential local-density approxima tion to search for the stable atomic and electronic structure. We find that surface dimers indeed form, accompanied by a large energy gain elf 0.618 e V/(surface atom) with respect to the ideal surface. As in Si and Ge, the di mer is buckled, but in alpha-Sn the amount of buckling is surprisingly larg e, 1.0 Angstrom, to be compared with 0.4 Angstrom (Si) and 0.74 Angstrom (G e). A frozen phonon calculation predicts a corresponding surface dimer rock ing mode at 4.8 THz. The surface core-level shift was found to be 0.6 eV fo r the up-dimer atom. In the ground state of alpha-Sn(100) we find that dime rs tend to order "atniferromagnetically." Calculations show that the most f avored states with asymmetric buckled dimers are the c(4 x 2) and p(2 x 2) antiferro reconstructions, found to be nearly degenerate. Results are discu ssed in connection with existing and future experiments. [S0163-1829(98)061 43-8].