iDMRG for spinful fermions

Question

H!
I would like to do an infinite DMRG implementation for a fermionic Hamiltonian with spin. It is not clear to me how to construct an MPO for this model. I have gone through the sample file Heisenberg .h, but it would be really helpful if you could point me to some documentation or sample code on implementing iDMRG for fermions.

I want to be able to get the correlations in the asymptotic limit so is it better to do finite DMRG and a finite-size scaling or should I use infinite dmrg for this purpose? Also will iDMRG algorithm work for systems with impurities ?

Thank You!

Answer 1

I'll give a quick answer and I'm sure Miles can expand on it. You would have to make the MPO manually as explained here: http://itensor.org/docs.cgi?page=tutorials/MPO

There is an open issue about making this more automated with AutoMPO but we haven't incorporated it yet: https://github.com/ITensor/ITensor/pull/161

However, I would definitely suggest trying out finite DMRG and using finite-size scaling first. It will be a lot easier to set up, and there isn't much of a disadvantage.

To answer the question about impurities, the standard iDMRG algorithm is not designed for impurities. I think the way to do it would be to first solve the problem with iDMRG without the impurity, then solve the impurity problem on a "finite" system using the solution from iDMRG to set the boundary conditions.

Comments

Thank You for the answer and clarifications. I think I'll do a finite-size scaling analysis first and see if I'm getting some reliable results.  When I go to this link 'http://itensor.org/docs.cgi?page=tutorials/handMPO&vers=cppv3' to learn how to construct MPO manually it says 'Documentation file not found'.

Best Regards