MPS for MixedSiteSet with different QN conservation on subsystems

Question

Hi everyone,

I am trying to implement a system with mixed Sites ( two bosonic sites at positions i, j, the rest fermionic spin 1/2 sites). The bosonic sites should not conserve QNs, the fermionic sites do.
I pass arguments like {"ConserveQNs",true} to the fermionic subsystem and {"ConserveQNs", false, "MaxOcc", MaxOcc} to the bosonic subsystem.

Creating the SiteSet, creating an initial state InitState(siteset) and setting the different sites also works without an problem.
However the created state does not seem to work with the function MPS(state) to create an MPS from it. It gives a segmentation fault.
Is this because of the different QN conservation on the subsystems? And is there an easy fix/ alternative way to create an MPS from the SiteSet?

Thank you very much in advance for any help!

Comments

We would need to investigate this in more detail, but just a quick comment that making MPS with mixed types of sites is generally much easier and smoother in the Julia version. Do you have a particular reason for using the C++ version in this case?

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Thanks for the comment! I work with C++ as it is the program commonly used in my group and it is easier to compare with work done previously by others.

Answer 1

For anyone interested, I solved the issue by now by adding "empty" quantum numbers in the file ITensor/itensor/mps/sites/boson.h
Replacing one line
s = Index(1+maxOcc,tags);
with
s = Index(QN(),1+maxOcc,tags);
did the trick.