Conservation of quantum numbers in Hubbard sites

Question

Hi, all.
When I try
auto sites =Hubbard(N,{"ConserveSz",false,"ConserveNf",false});
, it shows following error:
One of ConserveSz or ConserveNf must be true for Hubbard sites
It seems there's no such physical constraint in Hubbard sites.
Why couldn't I set that there's no QN conserve?
Thanks.
Best,
Victor

Comments

Hi Victor,

If you don't want any QNs conserved, you should be able to use:

    auto sites = Hubbard(N,{"ConserveQNs=",false})

ConserveQNs=true by default, so unless you turn it off explicitly, the system will expect some sort of QN to be conserved. That is why you are getting the error when you turn off both ConserveSz and ConserveNf. I agree it is a bit confusing, perhaps what you tried should have the same result as ConserveQNs=false (I think one reason to not do that is if we add other kinds of symmetry, like fermion parity conservation, then Hubbard(N,{"ConserveSz",false,"ConserveNf",false}) could be taken to mean that parity is conserved).

Cheers,
Matt

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Hi, Matt.
It works. Thank you.

Answer 1

Please see the comments above for the answer.