August 2013 - Comp-phys-alps-users

Re: [ALPS-users] Question concerning an initial state in TEBD
by Joseph Prentice 08 Aug '13

08 Aug '13

Hi Michael, I see, I thought that might be the case. I know very little about Fortran, but if it's possible to set up this initial Hamiltonian/state, I'd like to give it a go, even if I am unable to get it to work. Could I have further details on this please? Thank you, Joseph On 7 Aug 2013, at 11:00, <comp-phys-alps-users-request(a)lists.phys.ethz.ch> wrote: > Send Comp-phys-alps-users mailing list submissions to > comp-phys-alps-users(a)lists.phys.ethz.ch > > To subscribe or unsubscribe via the World Wide Web, visit > https://lists.phys.ethz.ch/listinfo/comp-phys-alps-users > or, via email, send a message with subject or body 'help' to > comp-phys-alps-users-request(a)lists.phys.ethz.ch > > You can reach the person managing the list at > comp-phys-alps-users-owner(a)lists.phys.ethz.ch > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Comp-phys-alps-users digest..." > > > Today's Topics: > > 1. Question concerning an initial state in TEBD (Joseph Prentice) > 2. Re: Question concerning an initial state in TEBD (Michael Wall) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Tue, 6 Aug 2013 12:25:40 +0000 > From: Joseph Prentice <Joseph.Prentice(a)physics.ox.ac.uk> > To: "<comp-phys-alps-users(a)lists.phys.ethz.ch>" > <comp-phys-alps-users(a)lists.phys.ethz.ch> > Subject: [ALPS-users] Question concerning an initial state in TEBD > Message-ID: > <747861816F6A5C47BE50FCA07F5B2B4A0DF3D2(a)EXCHNG16.physics.ox.ac.uk> > Content-Type: text/plain; charset="us-ascii" > > Hi again all, > > I just had a short question about the TEBD code in ALPS. I would like to study the evolution of an initial state that is a Neel state, but rotated by an angle /alpha about the y-axis, under the XXZ Hamiltonian. A Hamiltonian whose ground state would be the right one would simply have a magnetic field along the direction of /alpha that swaps direction at each site i.e. (-1)^l *(cos /alpha *S^z_l + sin /alpha *S^x_l) where l is the site number, but I can't see a way to put this into the code. Is alternating the sign of the interaction in this way possible? > Also, if there is another way of producing such a state in the TEBD code, it would be wonderful if someone pointed it out, I would be very grateful. > > Thank you very much, > > Joseph Prentice > > ------------------------------ > > Message: 2 > Date: Tue, 6 Aug 2013 14:31:20 -0600 > From: Michael Wall <mwall.physics(a)gmail.com> > To: comp-phys-alps-users(a)lists.phys.ethz.ch > Subject: Re: [ALPS-users] Question concerning an initial state in TEBD > Message-ID: > <CA+DwVMoeLK_TfLEi4DGHCkG7riYn3MHOZz6=E3TaPLcxcekBLQ(a)mail.gmail.com> > Content-Type: text/plain; charset="iso-8859-1" > > Hi Joseph, > > At present, the only initial states supported by tebd are ground states of > translation-invariant Hamiltonians or the 'kink' initial state used in the > spin tutorials. You can edit the source file tebd.f90 to write in another > product state of your choice. If this is the route you would like to > follow I can give you more details. The next generation of MPS codes for > ALPS will include much greater flexibility in the choice of initial state. > > -Michael > > > On Tue, Aug 6, 2013 at 6:25 AM, Joseph Prentice < > Joseph.Prentice(a)physics.ox.ac.uk> wrote: > >> Hi again all, >> >> I just had a short question about the TEBD code in ALPS. I would like to >> study the evolution of an initial state that is a Neel state, but rotated >> by an angle /alpha about the y-axis, under the XXZ Hamiltonian. A >> Hamiltonian whose ground state would be the right one would simply have a >> magnetic field along the direction of /alpha that swaps direction at each >> site i.e. (-1)^l *(cos /alpha *S^z_l + sin /alpha *S^x_l) where l is the >> site number, but I can't see a way to put this into the code. Is >> alternating the sign of the interaction in this way possible? >> Also, if there is another way of producing such a state in the TEBD code, >> it would be wonderful if someone pointed it out, I would be very grateful. >> >> Thank you very much, >> >> Joseph Prentice >

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Question concerning an initial state in TEBD
by Joseph Prentice 06 Aug '13

06 Aug '13

Hi again all, I just had a short question about the TEBD code in ALPS. I would like to study the evolution of an initial state that is a Neel state, but rotated by an angle /alpha about the y-axis, under the XXZ Hamiltonian. A Hamiltonian whose ground state would be the right one would simply have a magnetic field along the direction of /alpha that swaps direction at each site i.e. (-1)^l *(cos /alpha *S^z_l + sin /alpha *S^x_l) where l is the site number, but I can't see a way to put this into the code. Is alternating the sign of the interaction in this way possible? Also, if there is another way of producing such a state in the TEBD code, it would be wonderful if someone pointed it out, I would be very grateful. Thank you very much, Joseph Prentice

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Entropy calculations for classical model using Quantum-Wang-Landau
by Vipin Varma 02 Aug '13

02 Aug '13

Dear all, I am trying to use the Quantum-Wang-Landau (QWL) algorithm to calculate the entropy of a linear chain spin-1/2 model with Jxy=0 in a field h=1, which is classical but QWL seems to be suggested for entropy calculations. However with forty sites and down to low temperatures, I don't seem to be getting near the correct entropy density result of S ~ 0.4812 ... The parameter file is <<<<<<<<<<<<<<<<<<<<<<<<<< LATTICE="chain lattice" MODEL="spin" local_S=1/2 h=1 J = 1 Jxy = 0 CUTOFF = 500 {L=40} <<<<<<<<<<<<<<<<<<<<<<<<< and a partial output of entropy density versus temperature is <SNIP> </PARAMETERS> <legend show="true"/> <xaxis label="Temperature"/> <yaxis label="Entropy Density"/> <set label=""> <point><x>0.10000000000000001</x><y>0.065628773413218822</y></point> <point><x>0.20000000000000001</x><y>0.13394955300729872</y></point> <point><x>0.30000000000000004</x><y>0.24229259030929573</y></point> <point><x>0.40000000000000002</x><y>0.31481859757794478</y></point> <point><x>0.5</x><y>0.39826073000393336</y></point> <point><x>0.59999999999999998</x><y>0.46128739087861204</y></point> <point><x>0.69999999999999996</x><y>0.50938492873462538</y></point> <point><x>0.79999999999999993</x><y>0.5481023575910553</y></point> <point><x>0.89999999999999991</x><y>0.57776445729654646</y></point> <point><x>0.99999999999999989</x><y>0.59988758184662683</y></point> <point><x>1.0999999999999999</x><y>0.61635447545226674</y></point> <SNIP> I have tried changing the lattice length and cut-off but not much changes. Any advice on what I might be doing wrong will be greatly appreciated. With regards, Vipin

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Re: [ALPS-users] Problem with having Sz conserved in TEBD quench
by Joseph Prentice 01 Aug '13

01 Aug '13

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(a)lists.phys.ethz.ch> wrote: > Send Comp-phys-alps-users mailing list submissions to > comp-phys-alps-users(a)lists.phys.ethz.ch > > To subscribe or unsubscribe via the World Wide Web, visit > https://lists.phys.ethz.ch/listinfo/comp-phys-alps-users > or, via email, send a message with subject or body 'help' to > comp-phys-alps-users-request(a)lists.phys.ethz.ch > > You can reach the person managing the list at > comp-phys-alps-users-owner(a)lists.phys.ethz.ch > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Comp-phys-alps-users digest..." > > > 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) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Wed, 31 Jul 2013 14:09:31 +0000 > From: Joseph Prentice <Joseph.Prentice(a)physics.ox.ac.uk> > To: "comp-phys-alps-users(a)lists.phys.ethz.ch" > <comp-phys-alps-users(a)lists.phys.ethz.ch> > Subject: [ALPS-users] Problem with having Sz conserved in TEBD quench > Message-ID: > <747861816F6A5C47BE50FCA07F5B2B4A0DE4C6(a)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 >

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