Ab initio optical properties of Si(100)

We compute the linear optical properties of different reconstructions of th e clean and hydrogenated Si(100) surface within DFT-LDA, using norm-conserv ing pseudopotentials. The equilibrium atomic geometries of the surfaces, de termined from self-consistent total-energy calculations within the Car-Parr inello scheme, strongly influence reflectance anisotropy spectra, showing d ifferences between the p(2 x 2) and c(4 x 2) reconstructions. The different ial reflectivity spectrum for the c(4x2) reconstruction shows a positive pe ak at (h) over bar omega<1 eV, in agreement with experimental results. [S01 63-1829(99)03928-4].