bilayer

sisl.geom.bilayer(bond: float = 1.42, bottom_atoms: sisl.typing.AtomsLike | None = None, top_atoms: sisl.typing.AtomsLike | None = None, stacking: Literal['AB', 'AA', 'BA'] = 'AB', twist=(0, 0), separation: float = 3.35, vacuum: float = 20, *, layer: Literal['both', 'bottom', 'top'] = 'both', ret_angle: bool = False) → Geometry

Commensurate unit cell of a hexagonal bilayer structure, possibly with a twist angle.

This routine follows the prescription of twisted bilayer graphene found in [13].

Notes

This routine may change in the future to force some of the arguments.

Parameters:

bond – bond length between atoms in the honeycomb lattice
bottom_atoms – atom (or atoms) in the bottom layer. Defaults to Atom(6)
top_atoms – atom (or atoms) in the top layer, defaults to bottom_atom
stacking – stacking sequence of the bilayer, where XY means that site X in bottom layer coincides with site Y in top layer
twist (tuple of int, optional) – integer coordinates (m, n) defining a commensurate twist angle
separation – distance between the two layers
vacuum – length of vacuum region (along 3rd lattice vector)
layer – control which layer(s) to return
ret_angle – return the twist angle (in degrees) in addition to the geometry instance