STRUCTURE AND ENERGETICS OF SEGREGATED AND NONSEGREGATED GE(001) SI(2X1)/

We present the results of ab initio pseudopotential density functional calculations for the geometry, energetics and electronic structure of the monolayer Si covered Ge(001)(2x1) surface. A segregated structure , in which Si occupies the second layer while Ge floats to the surface , is found to be energetically favorable by 0.38 eV per dimer compared to the nonsegregated Si-capped structure. In the latter case, the Si dimers are found to be asymmetric, with a bond length of 2.26 Angstrom and a tilt angle of 16.7 degrees, while in the segregated structure, the Ge dimers have a bond length of 2.39 Angstrom, and a tilt angle of 17.5 degrees. [S0163-1829(98)00712-7].