Hi Giuseppe,

I mean the result concerning the spin-spin correlation function but I agree, I don't have to specify Sz_total for the ferromagnetic case. However, this parameter is really important in the S=1 antiferromagnetic Heisenberg chain (due to the spins 1/2 before the first and after the last site).

Thanks a lot for your answer,

Julien


On 11/10/2016 15:09, Giuseppe Carleo wrote:
Hi Julien,

what do you mean that the results you get are wrong? 

I ran that script and found a reasonable ground-state energy ( i.e. E_0 ~ - L/4  ) 

If you’re concerned about the spin-spin correlations, you should be careful when specifying the subspace in which you’re looking for the ground-state : 

in your case you specified Sz_total = 0, which is not necessarily what you want to do when studying the ferromagnetic model. 


Giuseppe 






-------------------------------------
Dr Giuseppe Carleo

ETH Zurich 
Institute for Theoretical Physics
Wolfgang-Pauli-Str. 27
8093 Zurich - Switzerland

Office: HIT G 31.4
-------------------------------------




On 11 Oct 2016, at 14:25, Julien <julien.despres@institutoptique.fr> wrote:

Hello ALPS community,

First, sorry for my English and for the trivial question that I'm going
to ask you.
I already made the tutorial on the S=(1/2, 1) antiferromagnetic
Heisenberg chain where
I found the correlation function and the gap in the thermodynamic limit
(for S = 1). Now,
I'm trying to do the same thing for the S=1/2 ferromagnetic Heisenberg
chain but I guess I made
a mistake when we have to specify the different parameters. Here is what
I wrote in my computer
code :


parms.append({
    'LATTICE'                               : 'open chain lattice',
    'MODEL'                                 : 'spin',
    'CONSERVED_QUANTUMNUMBERS'              : 'N,Sz',
    'Sz_total'                              : 0,
    'J'                                     : -1,
    'SWEEPS'                                : 4,
    'NUMBER_EIGENVALUES'                    : 1,
    'L'                                     : 32,
    'MAXSTATES'                             : 20,
    'MEASURE_CORRELATIONS[Diagonal spin correlations]'      : 'Sz',
})

but the result is completely wrong. I only modify the sign of the
coupling constant compared to the antiferromagnetic case.


Thank you in advance for your help,

Best regards,
Julien



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