July 2007 - Comp-phys-alps-users

Re: [ALPS-users] Transverse Ising-Model
by armin.sauter＠uni-ulm.de 18 Jul '07

18 Jul '07

> Dirloop should not work on that model. I'll check this. > Did you not get an error message? No error messages. > You should never set CONSERVED_QUANTUMNUMBERS=Sz for > models that do not conserve Sz, such as your model. Sx(i)*Sx(j) = 1/2*exchange_xy + 1/4*(Splus(i)*Splus(j)+Sminus(i)*Sminus(j)) The results for the energy are the same without the second term. Could there be an automatic restriction of the base? The model and parameter files are attached. The 'chain lattice' is from the standard lattice library. thanks Armin

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ALPS 1.3b6
by Matthias Troyer 18 Jul '07

18 Jul '07

ALPS 1.3b6 has been released and is available for download from http://alps.comp-phys.org/ . Changes from 1.3b5 include: - more stringent tests on whether a spin model can be simulated by the QMC codes - a bug fix in the DMRG code for non-magnetization-conserving model Enjoy! Matthias Troyer

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Transverse Ising-Model
by Armin 13 Jul '07

13 Jul '07

I am trying to calculate the ground state energy of the transverse Ising-Model ( -J*Sx(i)*Sx(j)-h*Sz(i) ) on a simple 1d-chain-lattice with the DMRG and DIRLOOP applications. The results seems to be calculated with a constrained basis even without the CONSERVED_QUANTUMNUMBERS="Sz" parameter (compared to the FULLDIAG where the parameter has its effect on the results). It looks more like the half of a XY-model. So my question is if there is a special problem with the DMRG and DIRLOOP applications and the Ising-Model. Btw, wenn changing the x- and z-axis then the LOOP application gets the same results as the FULLDIAG, but DIRLOOP aborts with an 'Did not find raising and lowering operators' error. best regards, Armin

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Re: [ALPS-users] Comp-phys-alps-users Digest, Vol 16, Issue 1
by John Single 06 Jul '07

06 Jul '07

AH yes. I am sorry, it is version 1.2. So if distance doesn't matter, then a square lattice vs a rectangular lattice with the same coupling strengths are identical? I tried to run the simulations with both and they were semi-identical. -Thanks, John On 7/6/07, comp-phys-alps-users-request(a)phys.ethz.ch < comp-phys-alps-users-request(a)phys.ethz.ch> wrote: > > Send Comp-phys-alps-users mailing list submissions to > comp-phys-alps-users(a)phys.ethz.ch > > To subscribe or unsubscribe via the World Wide Web, visit > https://webmail.phys.ethz.ch/mailman/listinfo/comp-phys-alps-users > or, via email, send a message with subject or body 'help' to > comp-phys-alps-users-request(a)phys.ethz.ch > > You can reach the person managing the list at > comp-phys-alps-users-owner(a)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. Re: 2-D heisenberg system (Matthias Troyer) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Thu, 5 Jul 2007 21:48:37 -0600 > From: Matthias Troyer <troyer(a)phys.ethz.ch> > Subject: Re: [ALPS-users] 2-D heisenberg system > To: comp-phys-alps-users(a)phys.ethz.ch > Message-ID: <6958DCFB-7B75-4DD2-BDBD-7DE873973476(a)phys.ethz.ch> > Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed > > > On 28 Jun 2007, at 08:57, John Single wrote: > > > Hello, > > > > I am having a little difficulty understanding the tutorial > > for ALPS version 2. Is their a difference between the rectangular > > lattice and square lattice? If we set the coupling itself in 2d(J0 > > and J1) then does relative distance matter or is distance and > > coupling strength two separate factors that make up an effective > > coupling strength? > > > > -Thanks, John > > We do not have any ALPS version 2 yet. Do you mean ALPS 1.2 or ALPS > 1.3? The distance does not enter anywhere. > > The way it works is that you define different bond types in the > lattice (e.g. type 0,1,2) and then define Hamiltonian terms for each > bond type. These terms can have different coupling constants (e.g. J0 > and J1). There is a shortcut for that in version 1.3 and that's why I > first need to know which version you are referring to. > > Matthias > > > > > > End of Comp-phys-alps-users Digest, Vol 16, Issue 1 > *************************************************** >

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2-D heisenberg system
by John Single 06 Jul '07

06 Jul '07

Hello, I am trying to use alps version 2 to simulate a 2-D heisenberg spin ladder model with 2 different (ladder and rail) exchange strengths. In the example for a 1-D chain I changed the lattice to rectangular lattice but I guess that is not the right keyword. Is there an easy way to do this? Thanks, John

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