Hi, > a) Regarding the edge disorder, I cannot remove the disorder in the edges > with the leads (I saw your recent previous discussion)
I am not sure what you mean by this. From what I can see from your model
there is no disorder in your leads:
lead0 = kwant.Builder(sym0)
lead0[graphene.shape(lead0_shape, (0, 0))] = -pot
lead0[[kwant.builder.HoppingKind(*hopping) for hopping in nn_hoppings]] =
-t
lead0[[kwant.builder.HoppingKind(*hopping) for hopping in nnn_hoppings_a]]
= -nnn_hoppinga
lead0[[kwant.builder.HoppingKind(*hopping) for hopping in nnn_hoppings_b]]
= -nnn_hoppingb
Also, you do not need to manually enumerate all the hopping kinds like this.
Lattices have a method 'neighbors' that returns the hopping kinds for
neighboring sites in the lattice. You could reduce the above code to:
lead0[graphene.shape(lead0_shape, (0, 0))] = -pot
lead0[graphene.neighbors()] = -t
lead0[(kind.family_a == a for kind in graphene.neighbors(2))] =
-nnn_hoppinga
lead0[(kind.family_a == b for kind in graphene.neighbors(2))] =
-nnn_hoppingb
which would allow you to remove the lines where you explicitly enumerate the
hoppings:
nn_hoppings = (((0, 0), a, b), ((0, 1), a, b), ((-1, 1), a, b))
nnn_hoppings_a = (((-1, 0), a, a), ((0, 1), a, a), ((1, -1), a, a))
nnn_hoppings_b = (((1, 0), b, b), ((0, -1), b, b), ((-1, 1), b, b))
> Is it possible already to compute directly from Kwant the local current
> density? If yes, how?
This will be available in Kwant version 1.3. I see that at the start of your
script that you have the line 'from __future__ import division' which tells
me that you are still using Python 2. Since version 1.2 Kwant supports Python 3
only, and the 1.1.x versions will only receive bug fixes, no new features.
For this reason I would recommend using Python 3 unless you have a good
reason not to.
Coming back to your question, while calculating currents will be available
in Kwant 1.3, if your model only has 1 orbital per site, it is probably
just as easy to calculate the current manually. The current flowing
from site 'j' to site 'i' is written:
J_ij = 2 Im{(ψ_i)* H_ij ψ_j}
where 'ψ_i' is the component of the wave function on site 'i', '*' is
complex conjugation, and 'H_ij' is the Hamiltonian matrix element
between sites 'i' and 'j'. In Kwant this could be computed like:
psi = kwant.wave_function(syst)(0)[0] # scattering state 0 from lead 0
current = np.array([2 * psi[i].conjugate() * syst.hamiltonian(i, j) * psi[j]
for i, j in syst.graph])
current = current.imag
In Kwant version 1.3 there will also be functionality for plotting such
quantities defined on hoppings.
Hope that helps,
Joe
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