A self-consistent pseudopotential method is used to calculate the electronic structure of the (001) surface of Si. The results for the ideal 1 × 1 surface are discussed in terms of density-of-states curves and charge-density distributions and compared with earlier calculations. The calculation for the reconstructed surface is based on the geometry recently obtained by Jona et al. using a low-energy-electron-diffraction (LEED) intensity analysis. It assumes that the surface reconstructs in a 2 × 1 pattern by forming zig-zag chains along the  or  direction of the surface plane. Although this geometry agrees with observed LEED spectra far better than any of the previously discussed reconstructions, our calculation yields a metallic surface for this geometry. This results primarily from surface states which arise from broken bonds in the surface and the second atomic layer. In addition, the calculated local density of states near the surface is not consistent with existing photoemission data. © 1978 The American Physical Society.