Relaxation of the rocksalt (001) surface: Alkali halides, MgO, and PbS

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Abstract
We evaluate the static relaxation of the (001) face of rocksalt-structured ionic crystals, using shell models. The results for moderately polarizable compounds, namely, the alkali halides and MgO, are in qualitative agreement with those of earlier calculations but overall somewhat smaller. PbS is treated as an example of highly polarizable substances close to an instability. The results for PbS show a larger and deeper penetrating relaxation than in the case of the alkali halides. Preliminary results for PbTe, which has a large (T-dependent) anion polarizability, show a precursor of a total crystal reconstruction. It is conjectured that in such cases the lowered symmetry at the surface can act as a trigger for a structural phase transition.