kwant.lattice.Monatomic

class kwant.lattice.Monatomic(prim_vecs, offset=None, name='', norbs=None)

Bases: kwant.system.SiteFamily, kwant.lattice.Polyatomic

A Bravais lattice with a single site in the basis.

Instances of this class provide the SiteFamily interface. Site tags (see SiteFamily) are sequences of integers and describe the lattice coordinates of a site.

Monatomic instances are used as site families on their own or as sublattices of Polyatomic lattices.

Parameters

• prim_vecs (2d array-like of floats) – Primitive vectors of the Bravais lattice.

• offset (vector of floats) – Displacement of the lattice origin from the real space coordinates origin.

``offset``

Displacement of the lattice origin from the real space coordinates origin

Type

vector

Methods

closest(pos)

Find the lattice coordinates of the site closest to position pos.

n_closest(pos, n=1, group_by_length=False, rtol=1e-09)

Find n sites closest to position pos.

Returns

sites – An array with sites coordinates.

Return type

numpy array

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

Return n-th nearest neighbor hoppings.

Parameters

• n (integer) – Order of the hoppings to return. Note that the zeroth neighbor is the site itself or any other sites with the same position.

• eps (float) – Tolerance relative to the length of the shortest lattice vector for when to consider lengths to be approximately equal.

Returns

hoppings – The n-th nearest neighbor hoppings.

Return type

list of kwant.builder.HoppingKind objects

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.

normalize_tag(tag)

Return a normalized version of the tag.

Raises TypeError or ValueError if the tag is not acceptable.

normalize_tags(tags)

Return a normalized version of the tags.

Raises TypeError or ValueError if the tags are not acceptable.

pos(tag)

Return the real-space position of the site with a given tag.

positions(tags)

Return the real-space positions of the sites with the given tags.

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 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 (1d array-like) – The real-space origin for the flood-fill algorithm.

Returns

shape_sites

Return type

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()
>>> syst = kwant.Builder()
>>> syst[lat.shape(circle, (0, 0))] = 0
>>> syst[lat.neighbors()] = 1

vec(int_vec)

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

Parameters

vec (integer vector) –

Returns

output

Return type

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 Builder instances. See example below.

Parameters

• center (1d array-like of floats) – 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

(sequence of vectors) Primitive vectors

prim_vecs[i]` is the i-th primitive basis vector of the lattice displacement of the lattice origin from the real space coordinates origin.