I hope somebody else could give you a better answer, but I don’t think this is possible out of the box, and I’m not 100% sure it is at all possible in the way you think about it.

What I would try is away to play around with a new model definition where you make a composite quantum number explicit.
The "fermion Hubbard” and “alternative fermion Hubbard” could be of inspiration for how to conserve N and/or Sz instead of Nup and/or Ndown.


Best,
Michele


--
ETH Zurich
Dr. Michele Dolfi
Institute for Theoretical Physics
HIT G 32.4
Wolfgang-Pauli-Str. 27
8093 Zurich
Switzerland


+41 44 633 78 56 phone
+41 44 633 11 15 fax 






On Jan 17, 2017, at 4:10 PM, Axel Gagge <axel.gagge@fysik.su.se> wrote:

​Hello, I just wanted to ask if it is possible to preserve a combination of quantum numbers such as the total number of excitations:

N = \sum_{bosonic sites} n_j + 1/2 \sum_{spinful sites} s_z

and what the syntax for this would be? I guess that one option would be to define a new quantum number and let Splus raise it by 1/2 but I just thought that I would check this with you first!

Otherwise, thank you for an excellent library! I have had no problems so far with the new release.

Thanks,
/Axel Gagge
First year PhD Student, Stockholm University


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