?It wasn't very hard to define such a quantum number, but it seems like it actually makes the simulation run much slower. I suppose this is because another quantum number needs to be stored which leads to a larger basis size again? On the other hand, I can think of no way to properly define the spin operators without using the quantum numbers S, Sz... ? Many thanks, Axel ________________________________ Från: Comp-phys-alps-users <comp-phys-alps-users-bounces@lists.phys.ethz.ch> för Matthias Troyer <troyer@phys.ethz.ch> Skickat: den 17 januari 2017 19:42 Till: comp-phys-alps-users@lists.phys.ethz.ch Ämne: Re: [ALPS-users] Conserve quantum number for composite unit cell You need to define a new combined quantum number, which is changed by the training and lowering operators for both types of particles. On 17 Jan 2017, at 08:54, Michele Dolfi <dolfim@phys.ethz.ch<mailto:dolfim@phys.ethz.ch>> wrote: 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 dolfim@phys.ethz.ch<mailto:dolfim@phys.ethz.ch> www.itp.phys.ethz.ch<http://www.itp.phys.ethz.ch/> +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<mailto: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 ---- Comp-phys-alps-users Mailing List for the ALPS Project http://alps.comp-phys.org/ List info: https://lists.phys.ethz.ch//listinfo/comp-phys-alps-users Archive: https://lists.phys.ethz.ch//pipermail/comp-phys-alps-users Unsubscribe by writing a mail to comp-phys-alps-users-leave@lists.phys.ethz.ch<mailto:comp-phys-alps-users-leave@lists.phys.ethz.ch>. ---- Comp-phys-alps-users Mailing List for the ALPS Project http://alps.comp-phys.org/ List info: https://lists.phys.ethz.ch//listinfo/comp-phys-alps-users Archive: https://lists.phys.ethz.ch//pipermail/comp-phys-alps-users Unsubscribe by writing a mail to comp-phys-alps-users-leave@lists.phys.ethz.ch.