Dear Adel,
Thank you for your quick reply. My problem is not about calculating the current in a specific region in the sample. I want to calculate a current which has an operator depends on the direction of the bond. This is similar to the spin current projected on a position-dependent spin-axis  as in section 2.7 in the manual. The position-dependent spin-axis depends on one site only, according to my understanding. I would like to know if it is possible to have position-dependent spin-axis depending on two sites of a bond. 
Regards
KS 

On 27 Jul 2020, at 8:47 PM, Abbout Adel <abbout.adel@gmail.com> wrote:

Dear Chan,

The current is calculated along a hopping for a kwant system. This means that it is calculated on any couple of sites hop=(site1,site2).

So if you provide a list of hoppings  L=[(site1,site2), (site3,site4),(site6, site73)], the kwant module will return the currents for those hoppings.

I hope this helps,
Adel

On Mon, Jul 27, 2020 at 3:36 PM Prof. CHAN Kwok Sum <apkschan@cityu.edu.hk> wrote:
Dear Kwant developer,
I want to define a spatially varying current operator which depends on the two sites of a bond. Can this be done giving the “onsite” a function in the current operator definition. According to the manual, the function for onsite has the signature of a Hamiltonian on-site function, does it mean the function can only have one site as its input and cannot have two sites of a bond as input? If “onsite” cannot do the job, any suggestion of how to solve the problem?
Regards,
KS Chan


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Abbout Adel