Hello,

What is the difference between   hop[0].tag   and hop[1].tag

hop[0].tag is the tag of the first site in the hopping and hop[1].tag is the tag of the second site in the hopping.

My second question 

the onsite fuction for example: def onsite(site, V):return V

why it depends on site where the shape functions for example 

def circle(pos): rsq = pos[0] ** 2 + pos[1] ** 2

depends on pos

Because  when creating a shape in realspace you typically only care about the position, whereas your onsite matrix elements could potentially depend on other things (e.g. the lattice that the site is from)

Happy Kwanting,

Joe