Re: [ALPS-users] Problem with having Sz conserved in TEBD quench - Comp-phys-alps-users

1 Aug 2013

      Thank you very much Michael! I had tried to do that, but I'd got a bit confused with the naming. In DMRG, to specify the total Sz, you used the name 'Sz_total', but I see it's different in TEBD.
Thanks again,
Joseph
On 1 Aug 2013, at 11:00, comp-phys-alps-users-request@lists.phys.ethz.ch
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Today's Topics:

Problem with having Sz conserved in TEBD quench (Joseph Prentice)
Re: Problem with having Sz conserved in TEBD quench (Michael Wall)

Message: 1
Date: Wed, 31 Jul 2013 14:09:31 +0000
From: Joseph Prentice Joseph.Prentice@physics.ox.ac.uk
To: "comp-phys-alps-users@lists.phys.ethz.ch"
   comp-phys-alps-users@lists.phys.ethz.ch
Subject: [ALPS-users] Problem with having Sz conserved in TEBD quench
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   747861816F6A5C47BE50FCA07F5B2B4A0DE4C6@EXCHNG16.physics.ox.ac.uk
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Hello all again,
I have been having a problem with my results for quenching a spin-1/2 XXZ model in the TEBD code and both my colleagues and I are stumped. I am attempting to study a quench from Delta = 4 to 2 in the XXZ model, starting from the ground state of the original Hamiltonian, and looking at the local magnetisation and correlation functions that result. I tried this out in small systems (around L=32), following the tutorials very closely and adapting them to my situation, and looking at the local magnetisation. When I included S_z (the total S_z) as a conserved quantum number in my parameters, I got no time dependence in my results, with each S_z being 1/2 everywhere along the chain for every time, which seems to be nonsensical. However, when I removed this constraint, I got (after a much longer simulation) more sensible results, with a time-dependence and the results being closer to 0. I am fairly certain that S_z should be conserved here, so my question is why does this not seem t
o work? I followed the tutorials very closely, and those scripts seem to work well enough. The parameter section of my script is as follows:
import pyalps
import matplotlib.pyplot as plt
import pyalps.plot
import numpy as np
import copy
parms = [ {
   'L'                : 32,
   'MODEL'                : 'spin',
   'local_S'            : 0.5,
   'Jxy'                : 1,
   'Jz'                : 4.0,
   'ITP_CHIS'            : [40, 40, 40],
   'ITP_DTS'            : [0.05, 0.05, 0.025],
   'ITP_CONVS'            : [1E-9, 1E-9, 1E-10],
   'INITIAL_STATE'            : 'ground',
   'CHI_LIMIT'            : 40,
   'TRUNC_LIMIT'            : 1E-12,
   'NUM_THREADS'            : 1,
   'TAUS'                : [0.0, 50.0],
   'POWS'                : [0.0, 1.0],
   'GS'                : ['Jz', 'Jz'],
   'GIS'                : [4.0, 2.0],
   'GFS'                : [2.0, 2.0],
   'NUMSTEPS'            : [100, 2500],
   'STEPSFORSTORE'            : [5, 5]
   } ]
baseName = 'Jz4to2Quench1L32'
nmlname = pyalps.writeTEBDfiles(parms, baseName)
res = pyalps.runTEBD(nmlname)
Data = pyalps.load.loadTimeEvolution(pyalps.getResultFiles(prefix = 'Jz4to2Quench1L32'), measurements = ['Local Magnetization'])
Any help would be greatly appreciated, as my simulations would be much faster if I could include this!
Thanks,
Joseph Prentice