How to use ITensor to compute the hamiltonian containing pairing terms

Question

Hi, I am using dmrg to compute the energy of some hamiltonian containing C^\dagC^\dag and CC. However as the dmrg runs, the energy can not converge to a fixed value. Can I use dmrg in this case?

Answer 1

Hi, you can definitely use ITensor dmrg for this kind of Hamiltonian, as I did in a project a while back (see http://arxiv.org/abs/1104.5493 ).

A key step is that you must set the "ConserveNf" option to false when creating the "sites" site set object.

See here: http://itensor.org/docs.cgi?page=classes/spinless
for documentation on the Spinless site set and
here: http://itensor.org/docs.cgi?page=classes/hubbard
for documentation on the Hubbard (fermions with spin) site set.

With these, and with the correct signs defining your Hamiltonian (remember that inside of AutoMPO the C and Cdag operators do anticommute), you should be able to use AutoMPO and dmrg just fine.

Please let me know if this doesn't fix your issue and I can take a look at your code if needed.

Best,
Miles

Comments

Thank you very much for your swift reply and it solves my problem.