Hubbard-Holstein 2-RDM Properties

[iavdic]

Hi Huanchen,

When using the get_2pdm() function with, for example, the MPS from the Hubbard-Holstein model, are the bosonic degrees of freedom traced out and the output 2-RDM is purely a fermionic one, or is the output a fermion-boson 2-RDM?

Thanks!

[hczhai]

Thanks for your interest in the block2 package.

For the Hubbard-Holstein model, the 2PDM is not a well-defined quantity, and you will get runtime error if you call driver.get_2pdm directly for the MPS from the Hubbard-Holstein model. You may compute the individual 2PDM elements using driver.expectation instead.

[iavdic]

Okay, thanks!