THE SURFACES OF BERYLLIUM

Beryllium is unique among metals. The isolated Be atom has a closed-shell 1s(2)2s2 configuration resulting is a weakly bound dimer. Promotion of the s-electrons into the unoccupied p-bands causes bonding in the solid, resulting in a solid with distinct properties: a high cohesive energy (3.32 eV per atom), a small lattice constant (2.29 angstrom), and a low density (1.85 gm/cm3). The reduction in coordination at the surface can have severe effects, because in this material there is always a competition between the energy required for s->p promotion and the energy gained from bonding. The static and dynamical properties of clean Be surfaces can be described in terms s->p promotion. Experimental results for the atomic structure, electronic states, and phonons at the surface of Be are compared with theoretical calculations.