[ALPS-users] Conserve quantum number for composite unit cell

[Matthias Troyer]

Have you tried using a grandcanonical instead of fixing the quantum number?

> On 18 Jan 2017, at 09:15, Axel Gagge <axel.gagge at fysik.su.se> wrote:
> 
> ​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 at lists.phys.ethz.ch <mailto:comp-phys-alps-users-bounces at lists.phys.ethz.ch>> för Matthias Troyer <troyer at phys.ethz.ch <mailto:troyer at phys.ethz.ch>>
> Skickat: den 17 januari 2017 19:42
> Till: comp-phys-alps-users at lists.phys.ethz.ch <mailto:comp-phys-alps-users at 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 at phys.ethz.ch <mailto:dolfim at 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 at phys.ethz.ch <mailto:dolfim at phys.ethz.ch>
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>> 
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>> 
>> 
>> 
>> 
>> 
>> 
>>> On Jan 17, 2017, at 4:10 PM, Axel Gagge <axel.gagge at fysik.su.se <mailto:axel.gagge at 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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> 
> <my_models.xml><my_lattices.xml><Test of iDMRG.ipynb>
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