Inter-layer interactions and the origin of SiC polytypes

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Abstract
The authors investigate, up to the fourth-nearest neighbour, the interaction energies J1 to J4 between SiC double layers by calculating the total energies of five SiC polytypes with norm-conserving pseudopotentials. They find J1=1.89 mod J2 mod with J2 negative. This is very close to the multi-phase degeneracy point J1=2 mod J2 mod in the ANNNI model at T=0 where an infinite number of polytypes are degenerate. The third-(J3) and fourth-(J4) neighbour interactions turn out to be very small but they stabilise the phase (3) (in Zhdanov notation) which has the lowest energy of those considered. The splitting of the multi-phase degeneracy and the origin of polytypes as possible equilibrium phases are discussed.
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