Dear Mohit,
I see the formula you are mentioning using the matsubara frequencies.
To use that expression, you need to use imaginary energies.
The steps are;
Sites1=[lat(5,j) for j in range(W)] # the sites where to mount lead 2
Sites2=[lat(6,j) for j in range(W)] # the sites where to mount lead 3
mount_vlead(sys, Sites1, 4) # number of orbitals =4. Here we mount lead
number 2
mount_vlead(sys, Sites2, 4) # number of orbitals =4. Here we mount lead
number 3
syst=sys.finalized()
G12=greens_function(syst, energy=-1.8*1j, in_leads=[3],out_leads=[2],
check_hermiticity=False).data
G21=greens_function(syst, ,energy=-1.8*1j, in_leads=[2],out_leads=[3],
check_hermiticity=False).data
H12=syst.hamiltonian_submatrix(to_sites=Sites1, from_sites=Sites2)
H21=syst.hamiltonian_submatrix(to_sites=Sites2, from_sites=Sites1)
Notices that, we had to use "check_hermiticity=False" because for these
complex energies, the system is not hermitian
Trace(np.dot(H21, G12)-np.dot(H12,G21) )) # check if the order is correct.
I hope this helps.
Adel
On Wed, Jun 17, 2020 at 6:51 PM
Dear Abbout, I apologize for not being clear in my question. My system is infinite (that is there are leads attached to the system) and I mounted virtual leads at points where I wanted kwant to evaluate green's function. Sorry about that.
The formula that I am using is from the supplementary material of the following paper: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.047702 It is possible that I am misinterpreting the formula as given in the paper as am very new to the subject.
I want to evaluate critical current in the Josephson Junction by maximizing current-phase dependency, for that I need total current in the system as a function of phase difference phi, I am not sure how to do that with local current operator in kwant.
Thank you for clarifying the output of green's function I am now sure that I was reading the output wrong which must have been the primary reason for getting zero.
I again apologize if I am not clear about what I am saying.
-- Abbout Adel