MULTILAYER RELAXATION OF THE MG(0001) SURFACE

We have investigated the interplanar relaxation of the clean (0001)-(1 x 1) surface of magnesium at 100 K using a dynamical LEED I-V analysi s. In contrast to almost all other metal surfaces, an expansion has be en observed for the first interlayer spacing of this clean surface. Us ing an extended database, the results indicate that the first three in terlayer spacings are relaxed from the bulk value by: DELTAd12 = +1.9 +/- 0.3%, DELTAd23 = +0.8 +/- 0.4%, and DELTAd34 = -0.4 +/- 0.5%. A co mparison of this observed multilayer relaxation with experimental and theoretical results for similar free-electron closepacked metal surfac es, e.g. Al(111), suggests that a surface expansion is a normal proper ty of high electron density simple metals.