RELAXATION OF THE CLEAN AND H-COVERED C(111) AND THE CLEAN SI(111)-1X1 SURFACES

Well-converged plane-wave pseudopotential calculations using a steepest-descent method of finding the optimum atomic and electronic configuration have been applied to the clean and H-covered C(111)-1x1 and the clean Si(111)-1x1 surfaces in diamond structure to give new values of the surface relaxations. The small relaxation found for C(111)-1x1-H agrees with low-energy electron diffraction (LEED) studies of this diamond surface and supports the explanation that the surface was H covered. The other relaxation results differ from previous work due to use of sufficiently high plane-wave cutoffs to assure convergence, but also due to use of more k points in the surface Brillouin zone and to use of the theoretical bulk lattice constant in the surface problem. Close agreement is found with LEED results for the relaxation of the impurity stabilized Si(111)-1x1 surface. Indications of metastability are found for both clean (111)-1x1 surfaces.