The nature of interplanar interactions in SiC polytypes

The stability of SiC polytypes has been discussed elsewhere in terms of successive, pairwise, interplanar interactions J n between Ising-like pseudo-spins. Here the model is first critically re-examined to resolve some doubts about the generality of the energy expression and the meaning of the J n . The original expression is validated as the correct most general form, with the four-spin coupling term K re-interpreted as a modification of the third-neighbour interaction depending on the local geometry. Secondly the authors note the moderately long range of the interaction to third-neighbour atomic double layers found in density functional calculations on Si and SiC. They argue that this can be interpreted as the remnant in the semiconductor of what would be Friedel oscillations in a metal.