kwant.lattice.Polyatomic

class kwant.lattice.Polyatomic(prim_vecs, basis, name='')

Bases: object

A Bravais lattice with an arbitrary number of sites in the basis.

Contains Monatomic sublattices. Note that an instance of Polyatomic is not itself a SiteFamily, only its sublattices are.

Parameters:

prim_vecs : sequence of sequences of floats

The primitive vectors of a Bravais lattice.

basis : sequence of sequences of floats

The coordinates of the basis sites inside the unit cell.

name : string or sequence of strings

The name of the lattice, or a list of the names of all the sublattices. If the name of the lattice is given, the names of sublattices are obtained by appending their number to the name of the lattice.

Raises:

ValueError

If dimensionalities do not match.

Attributes

prim_vecs	(sequence of vectors) prim_vecs[i] is the i-th primitive basis vector of the lattice
sublattices	(list of Monatomic) Sublattices belonging to this lattice.

Methods

neighbors(n=1, eps=1e-08)

Return n-th nearest neighbor hoppings.

Parameters:

n : integer

Order of the hoppings to return.

eps : float

Tolerance relative to the length of the shortest lattice vector for when to consider lengths to be approximately equal.

Returns:

hoppings : list of kwant.builder.HopplingKind objects

A list n-th nearest neighbor hoppings.

Notes

The hoppings are ordered lexicographically according to sublattice from which they originate, sublattice on which they end, and their lattice coordinates. Out of the two equivalent hoppings (a hopping and its reverse) only the lexicographically larger one is returned.

shape(function, start)

Return a key for all the lattice sites inside a given shape.

The object returned by this method is primarily meant to be used as a key for indexing kwant.Builder instances. See example below.

Parameters:

function : callable

A function of real space coordinates that returns a truth value: true for coordinates inside the shape, and false otherwise.

start : float vector

The origin for the flood-fill algorithm.

Returns:

shape_sites : function

Notes

When the function returned by this method is called, a flood-fill algorithm finds and yields all the lattice sites inside the specified shape starting from the specified position.

A Symmetry or Builder may be passed as sole argument when calling the function returned by this method. This will restrict the flood-fill to the fundamental domain of the symmetry (or the builder’s symmetry). Note that unless the shape function has that symmetry itself, the result may be unexpected.

Examples

>>> def circle(pos):
...     x, y = pos
...     return x**2 + y**2 < 100
...
>>> lat = kwant.lattice.honeycomb()
>>> sys = kwant.Builder()
>>> sys[lat.shape(circle, (0, 0))] = 0
>>> sys[lat.neighbors()] = 1

vec(int_vec)

Return the coordinates of a Bravais lattice vector in real space.

Parameters:vec : integer vector Returns:output : real vector

wire(center, radius)

Return a key for all the lattice sites inside an infinite cylinder.

This method makes it easy to define cylindrical (2d: rectangular) leads that point in any direction. The object returned by this method is primarily meant to be used as a key for indexing kwant.Builder instances. See example below.

Parameters:

center : float vector

A point belonging to the axis of the cylinder.

radius : float

The radius of the cylinder.

Notes

The function returned by this method is to be called with a TranslationalSymmetry instance (or a Builder instance whose symmetry is used then) as sole argument. All the lattice sites (in the fundamental domain of the symmetry) inside the specified infinite cylinder are yielded. The direction of the cylinder is determined by the symmetry.

Examples

>>> lat = kwant.lattice.honeycomb()
>>> sym = kwant.TranslationalSymmetry(lat.a.vec((-2, 1)))
>>> lead = kwant.Builder(sym)
>>> lead[lat.wire((0, -5), 5)] = 0
>>> lead[lat.neighbors()] = 1

Attributes

prim_vecs