Lattice relaxation at na(100) and na(110) surfaces

The surface relaxation of the first interlayer spacing for both the (110) and (100) faces of Na has been calculated selfconsistently using the density functional formalism and a new density matrix method which obviates the use of wavefunctions. For the Na(110) surface we find no relaxation of the first interlayer spacing in agreement with LEED studies, while for the Na(100) surface we predict a 2% reduction. Force constants for the movement of the last atomic layer are also determined.