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> wrote:

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Today's Topics:

1. Problem with having Sz conserved in TEBD quench (Joseph Prentice) 2. Re: Problem with having Sz conserved in TEBD quench (Michael Wall)

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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 Message-ID: <747861816F6A5C47BE50FCA07F5B2B4A0DE4C6@EXCHNG16.physics.ox.ac.uk> Content-Type: text/plain; charset="us-ascii"

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