Dear Santu Baidya,

The antiferromagnetic (positive J) Heisenberg model on the kagome lattice has frustration.
This causes the so-called negative sign problem in the quantum Monte Carlo methods.
Although the loop code can simulate such a system and produce some numbers, the errorbar
becomes very large especially at low temperatures.

You can use the exact diagonalization for the frustrated spin models, but the lattice size is
very limited in this case due to the spin size S=3/2.

Best,
Synge


> 2018/08/03 14:10、S Baidya <santubaidya2009@gmail.com>のメール:

>
> Dear Alps users,
>
>   I am totally new to ALPS code using quantum monte carlo. I have started to use this code for few small purpose like magnetic suceptibility vs temperature for various spin lattice models.
>
> Currently I have used ALPS code for calculating susceptibility for ising type S=3/2 Kagome lattice. I found in the lattice library that Kagome lattice is defined. So in the tutorial mc-02-susceptibilities/ I changed tutorial2d.py by editing
>
> #prepare the input parameters
> parms = []
> for t in [0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.25, 1.5, 1.75, 2.0]:
>     parms.append(
>         {
>           'LATTICE'        : "Kagome lattice",
>           'MODEL'          : "spin",
>           'local_S'        : 1.5,
>           'T'              : t,
>           'J'             : 4.2 ,
>           'THERMALIZATION' : 5000,
>           'SWEEPS'         : 50000,
>           'L'              : 60,
>           'ALGORITHM'      : "loop"
>         }
>     )
>
> Then I changed the same way param2d file and ran the alpspython tutorial2d.py and I got strange error
>
>
> /usr/local/lib/python2.7/dist-packages/matplotlib/style/core.py:203: UserWarning: In /usr/share/matplotlib/stylelib/classic.mplstyle: text.dvipnghack is obsolete. Please remove it from your matplotlibrc and/or style files.
>   warnings.warn(message)
> loop parm2d.in.xml
> ALPS/looper version 3.2b12-20100128 (2010/01/28)
>   multi-cluster quantum Monte Carlo algorithms for spin systems
>   available from http://wistaria.comp-phys.org/alps-looper/
>   copyright (c) 1997-2010 by Synge Todo <wistaria@comp-phys.org>
>
> using ALPS/parapack scheduler
>   a Monte Carlo scheduler for multiple-level parallelization
>   copyright (c) 1997-2016 by Synge Todo <wistaria@comp-phys.org>
>
> based on the ALPS libraries version 2.3.0
>   available from http://alps.comp-phys.org/
>   copyright (c) 1994-2016 by the ALPS collaboration.
>   Consult the web page for license details.
>   For details see the publication:
>   B. Bauer et al., J. Stat. Mech. (2011) P05001.
>
> [2018-Aug-03 14:02:51]: starting scheduler on cces-System-Product-Name
>   master input file  = /home/cces/kagome-alps/mc-02/parm2d.in.xml
>   master output file = /home/cces/kagome-alps/mc-02/parm2d.out.xml
>   termination file   = [disabled]
>   total number of thread(s) = 1
>   thread(s) per clone       = 1
>   number of thread group(s) = 1
>   auto evaluation = yes
>   time limit = unlimited
>   interval between checkpointing  = 3600 seconds
>   interval between progress report = 600 seconds
>   interval between vmusage report = infinity
>   task range = all
>   worker dump format = hdf5
>   worker dump policy = running workers only
> [2018-Aug-03 14:02:51]: task status: total number of tasks = 15
>   new = 15, running = 0, continuing = 0, suspended = 0, finished = 0, completed = 0, skipped = 0
> [2018-Aug-03 14:02:51]: starting 1 threadgroup(s)
> [2018-Aug-03 14:02:51]: dispatching a new clone[1,1] on threadgroup[1]
> WARNING: model is classically frustrated
> WARNING: model has negative signs
>
>
>
> I donot understand the actual reason and how to solve this situation. I used this tutorial before and it worked for ladder spin lattice.
>
>
> Can anyone please tell me what should I do to solve this situation.
>
>
> Thanking you,
>
> Santu Baidya
>
>
>
>
>
>

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