def hexagon_ac(side_width, offset=(-a / 2, 0)):
"""Hexagon aligned with the armchair edges of graphene
Parameters
----------
side_width : float
Hexagon side width. It will be adjusted to make perfect armchair edges.
offset : array_like
The default value makes sure that a carbon hexagon is at the center
if the :func:`.monolayer()` lattice is used.
"""
# expected number of atoms on an armchair edge
side_atoms = math.ceil((side_width / a_cc + 1) * 2 / 3)
side_atoms += (side_atoms % 2) # it must be an even number
# set a better width value based on the calculated number of atoms
side_width = (3 / 2 * side_atoms - 1) * a_cc - a_cc / 2
x0 = side_width * math.sqrt(3) / 2
y0 = side_width
hexagon = pb.Polygon([(0, y0), (x0, y0 / 2), (x0, -y0 / 2), (0, -y0),
(-x0, -y0 / 2), (-x0, y0 / 2)], offset)
return hexagon
def hexagon_ac(side_width, lattice_offset=(-a / 2, 0)):
"""A graphene-specific shape which guaranties armchair edges on all sides
Parameters
----------
side_width : float
Hexagon side width. It may be adjusted slightly to ensure armchair edges.
lattice_offset : array_like
Offset the lattice so a carbon hexagon is at the center of the shape.
The default value is specific for :func:`.monolayer()` and :func:`.bilayer()`
lattices from this material repository.
"""
# expected number of atoms on an armchair edge
side_atoms = math.ceil((side_width / a_cc + 1) * 2 / 3)
side_atoms += (side_atoms % 2) # it must be an even number
# set a better width value based on the calculated number of atoms
side_width = (3 / 2 * side_atoms - 1) * a_cc - a_cc / 2
x0 = side_width * math.sqrt(3) / 2
y0 = side_width
hexagon = pb.Polygon([(0, y0), (x0, y0 / 2), (x0, -y0 / 2), (0, -y0),
(-x0, -y0 / 2), (-x0, y0 / 2)])
hexagon.lattice_offset = lattice_offset
return hexagon
def test_polygon_api():
with pytest.raises(RuntimeError) as excinfo:
pb.Polygon([[0, 0], [0, 1]])
assert "at least 3 sides" in str(excinfo.value)
def trapezoid(a, b, h):
return pb.Polygon([[-a / 2, 0], [-b / 2, h], [b / 2, h], [a / 2, 0]])
def rectangle(width, height):
x0 = width / 2
y0 = height / 2
return pb.Polygon([[x0, y0], [x0, -y0], [-x0, -y0], [-x0, y0]])