Brillouin zone of a two-dimensional triangular lattice
= Brillouin zone of a two-dimensional triangular lattice
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The reciprocal lattice of a two-dimensional triangular <Bravais lattice> is triangular, so its <Wigner-Seitz cell> is a regular hexagon. Opposite boundary points are identified modulo reciprocal-lattice translations, and the six corners fall into two inequivalent classes of three corners each, conventionally denoted $K$ and $K'$.