Re: [Kwant] Hopping for random sites

Oct. 2, 2019

      Dear Ali,

I am not sure if I understand your question but let me say this way:
You want to choose randomly some sites in your system.
You put  nn or nnn hoppings for those chosen sites.

method:

import random
Sites=list(syst.sites)       #define a list of your sites
Random_sites= random.choices(Sites, k=5)  # choose randomly 5 sites
sys[(hop for hop in sys.expand(graphene.neighbors(2)) if (hop[0] in
Random_sites or hop[1] in Random_sites) )]=-1
#(from all the hoppings of order 2, you choose the hopings
hop=(site1,site2) wwhere one of the two sites is in you list of random
sites.)
kwant.plot(sys, site_color=family_colors, site_lw=0.1, colorbar=False)

I hope this helps
Adel

##################################################################################

from __future__ import division  # so that 1/2 == 0.5, and not 0
from math import pi, sqrt, tanh

import kwant

import scipy.sparse.linalg as sla

from matplotlib import pyplot

sin_30, cos_30 = (1 / 2, sqrt(3) / 2)
graphene = kwant.lattice.general([(1, 0), (sin_30, cos_30)],
                                 [(0, 0), (0, 1 / sqrt(3))])
a, b = graphene.sublattices

def make_system(r=5, w=2.0, pot=0.1):

    #### Define the scattering region. ####
    # circular scattering region
    def circle(pos):
        x, y = pos
        return x ** 2 + y ** 2 < r ** 2

    sys = kwant.Builder()

    # w: width and pot: potential maximum of the p-n junction
    def potential(site):
        (x, y) = site.pos
        d = y * cos_30 + x * sin_30
        return pot * tanh(d / w)

    sys[graphene.shape(circle, (0, 0))] = potential

    # specify the hoppings of the graphene lattice in the
    # format expected by builder.HoppingKind
    hoppings = (((0, 0), a, b), ((0, 1), a, b), ((-1, 1), a, b))
    sys[[kwant.builder.HoppingKind(*hopping) for hopping in hoppings]] = -1

    return sys

pot = 0.1
sys = make_system(pot=pot)
syst=sys.finalized()

# To highlight the two sublattices of graphene, we plot one with
# a filled, and the other one with an open circle:
def family_colors(site):
    return 0 if site.family == a else 1

import random
Sites=list(syst.sites)
Random_sites= random.choices(Sites, k=5)
sys[(hop for hop in sys.expand(graphene.neighbors(2)) if (hop[0] in
Random_sites or hop[1] in Random_sites) )]=-1
kwant.plot(sys, site_color=family_colors, site_lw=0.1, colorbar=False)

On Mon, Sep 30, 2019 at 5:09 PM Ali Asgharpour <asgharpour@sabanciuniv.edu>
wrote:
...
Hello,
Would you please let me know how I can add nn and nnn hoppings for
random sites (not all) in graphene?
Best regards,
Ali
-- 
Abbout Adel