Hi dears, 

I am trying to study curved structures on Kwant and i've already done a code that gives me the coordinates for all atoms.
What I have done was to curve a graphene sheet. By now, I am trying to add the hoppings to its structure, but as my structure does not have "symmetry"
when I write down:

lat = kwant.lattice.general([(1,0,0), (0,1,0), (0,0,1)],norbs=3)

syst[sites[0], lat(surface[0][0],surface[1][0],surface[2][0])] = -t

where surface[0][0], surface[1][0], surface[2][0] are the coordinates x, y and z of the first atom and sites[0] is the first site.

I create a curved surface and make my Kwant Ambient as follow:

class SURFACE(kwant.builder.SimpleSiteFamily):
    def normalize_tag(self, tag):
        return tinyarray.array(tag, float)
    def pos(self, tag):
        return tag

atoms = SURFACE(norbs=3)
syst = kwant.Builder()
sites = []
for i in range(int(len(surface[0]))):
    x = surface[0][i]
    y = surface[1][i]
    z = surface[2][i]

My question is:

When I write  lat(surface[0][0],surface[1][0],surface[2][0]) it does not stay at the
real surface[0][0],surface[1][0],surface[2][0] position because it has floats values.

When I type lat(surface[0][0],surface[1][0],surface[2][0]) I see:

(Site(<class '__main__.SURFACE'>(None, 1), array([-3.472, -9.108, 1.205])), Site(kwant.lattice.Monatomic([[1.0, 0.0, 0.0], [0.0, 1.0, 0.0], [0.0, 0.0, 1.0]], [0.0, 0.0, 0.0], '', 3), array([-3, -9, 1])))

and array([-3, -9, 1]) should be array([-3.472, -9.108, 1.205]). Why lattices accept only integer values?