Dear Adel,

It seems that you did not get it correctly. A hopping is a tuple of two sites which make a bond in your lattice. So the direction is not important.

Hop=(site1,site2)

Hop[0]=site1

Hop[1]=site2

I suggest to you to have a look at the frequently asked questions in kwant [1]. It explains a lot of interesting things.

I hope this helps.

Regards,

Adel

[1] https://kwant-project.org/doc/1/tutorial/faq

On Mon, Sep 9, 2019 at 2:15 PM Adel Belayadi <adelphys@gmail.com> wrote:

Dear Joseph.

Thank you for your reply. If I got it well, you mean the first site the hopping along x direction and second site the hopping in the y direction.

Best

A.BELAYADI

Le lun. 2 sept. 2019 à 09:15, Joseph Weston <joseph.weston08@gmail.com> a écrit :

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

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Abbout Adel