Dear Wilson,
The proposed solution I have commented* on was wrong and it does not work
in your case since. **kwant.digest.uniform or **or random.uniform do
provide different values for A and B sulattices even if we fix the seed*.
In fact kwant defines the sublattice within the same tag with different
site values. For this reason,* the proposed solution will not work* *even
when including the sublattice condition in the onsite(site)* function
depending on the site variable
*The function **random.uniform will not work in your case anymore since you
can not set the tag variable there.*
In fact, the situation is somehow tricky. *So you need to use a tag as a
variable*. I have corrected your script and it is working now. You can use
site_color=family_color in kwant.plot() to see the opposite onsite value
with red and blue colors in your system. *You don't need to use low=0 and
high=+1 since we will use kwant.digest.uniform.*
*Here is the script and I hope it will be the correct solution looking for:*
import kwant
import numpy as np
from math import sqrt
import matplotlib.pyplot as plt
from types import SimpleNamespace
from ipywidgets import interact
from mpl_toolkits import mplot3d
import warnings
warnings.filterwarnings('ignore')
def onsite(site):
#we define a value which will be assined to both a and sublattices
v= 0.5 * kwant.digest.uniform(repr(site.tag)) + 0.5
return +v if site.family==sub_a else -v
r = 10
a=1
syst = kwant.Builder()
lat = kwant.lattice.honeycomb(a, norbs=1, name=['sub_a', 'sub_b'])
sub_a, sub_b = lat.sublattices
def circle(pos):
x, y = pos
return x ** 2 + y ** 2 < r ** 2
syst[lat.shape(circle, (0, 0))] = onsite
syst[lat.neighbors()] = 1
fsyst=syst.finalized()
# kwant.plot(fsyst)
H = fsyst.hamiltonian_submatrix(params=dict())
Es = np.linalg.eigvalsh(H)
plt.plot(Es, '.')
plt.show()
def family_color(site):
v= 0.5 * kwant.digest.uniform(repr(site.tag)) + 0.5
return +v if site.family==sub_a else -v
kwant.plot(syst, site_color=family_color, site_size=None, cmap='jet',
colorbar=True,fig_size=(15, 10))
plt.show()
best
Le mer. 25 mai 2022 à 20:21, Adel Belayadi <adelp...@gmail.com> a écrit :
> Dear Wilson,
> You said *I want to add random potentials on graphene. Within each unit
> cell, I want A site have the oppsite value to B site*.
> In fact you just need to set in the onsite function the sublattice
> dependence (I mean for instance *return +1 if site.family==a else -1.*)
>
> *SO in your case:*
> a, b =lat.sublattices
> def onsite(site,low, high):
> return *+1**np.random.uniform(low, high) if ifsite.family==*a* else
> -1*np.random.uniform(low, high)
>
> *or simply use the kwant.digest prebuilt function as*
> sites =list(syst.sites())
> Random_sites = random.choices(sites, k = 10)
> def onsite(site):
> return *+*0.5 *kwant.digest.uniform(repr(Random_sites)) + 0.5 if if
> site.family==aelse* -* 0.5 * kwant.digest.uniform(repr(Random_sites)) +
> 0.5
>
> I hope this will help.
>
> Best, Adel
>
> Le mer. 25 mai 2022 à 17:53, <wilson2...@outlook.com> a écrit :
>
>> Dear community,
>>
>> I want to add random potentials on graphene. Within each unit cell, I
>> want A site have the oppsite value to B site.
>> That is, random across unit cells, but symmetric respect to zero within
>> every unit cell. How to achieve this? I have tried to do so, but cannot
>> find a way.
>>
>> Below is my code:
>>
>> ```
>> import numpy as np
>> import kwant
>>
>> low = 0
>> high = 1
>> def make_syst(a=1):
>> syst = kwant.Builder()
>> lat = kwant.lattice.honeycomb(a, norbs=1, name=['a', 'b'])
>>
>> r = 10
>>
>> def circle(pos):
>> x, y = pos
>> return x ** 2 + y ** 2 < r ** 2
>>
>> def onsite(site, low, high):
>> return np.random.uniform(low, high)
>>
>> # first attempt using function, not working, also cannot gurantee a,
>> b are truly opposite in value
>> # syst[lat.a.shape(circle, (0, 0))] = onsite
>> # syst[lat.b.shape(circle, (0, 0))] = -1*onsite # wrong
>>
>> # second attempt, still not right
>> m = np.random.uniform(low, high)
>> syst[lat.a.shape(circle, (0, 0))] = m
>> syst[lat.b.shape(circle, (0, 0))] = -m
>>
>> syst[lat.neighbors()] = 1
>> return syst.finalized()
>>
>>
>> fsyst = make_syst()
>> # kwant.plot(fsyst)
>> H = fsyst.hamiltonian_submatrix(params=dict(high=high, low=low))
>> Es = np.linalg.eigvalsh(H)
>> plt.plot(Es, '.')
>> plt.show()
>> ```
>>
>> Thanks for help!
>>
>
