Comp-phys-alps-users September 2007

comp-phys-alps-users@lists.phys.ethz.ch

7 participants
11 discussions

DMRG question
by Justin David Peel 11 Dec '07

11 Dec '07

Hi all, I just have a quick question. How can I get the dmrg program to output the max truncation error during the final sweep (or any truncation error for that matter) to the output file? I know that it is output to the screen, but I would like it in the output file. Thanks, Justin

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Plot files
by Niall Moran 27 Sep '07

27 Sep '07

Hi, I am having some issues with the xml plot files. I want to generate a graph of susceptibility vs. magnetic field (gamma) for each of the lengths (L) used and each temperature (T). All the results from the simulations have been placed in the sqlite achive files results.db. The plot file I am trying to use is <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plot SYSTEM "conf/plot.dtd"> <plot name="Susceptibility versus Magnetic Field" output="xmgr"> <for-each name="L" > <for-each name="T" > <xaxis name="Gamma" type="parameter" /> <yaxis name="Susceptibility" type="mean" error="true" /> </for-each> </for-each> </plot> However when I try to use this with the command archive --verbose --command=plot --db-file=results.db --plot-file=plot_example.xml --output-path=. I get the following The Plotfile does not match the DTD! Fails parsing at: for-each name="L" > <for-each name="T" > <xaxis name="Gamma" type="parameter" /> <yaxis name="Susceptibility" type="mean" error="true" /> </for-each> </for-each> </plot> By taking out the second for-each tag and using <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plot SYSTEM "conf/plot.dtd"> <plot name="Susceptibility versus Magnetic Field" output="xmgr"> <for-each name="L" > <xaxis name="Gamma" type="parameter" /> <yaxis name="Susceptibility" type="mean" error="true" /> </for-each> </plot> it works but the graph does not make sense. I have also tried adding a constraint to pick out one particular temperature. <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plot SYSTEM "conf/plot.dtd"> <plot name="Susceptibility versus Magnetic Field" output="xmgr"> <for-each name="L" > <xaxis name="Gamma" type="parameter" /> <yaxis name="Susceptibility" type="mean" error="true" /> <constraint name="T" condition="=0.1" /> </for-each> </plot> This leads to the same error and says parsing fails at the same point. I am using ALPS 1.3b6. Any help is greatly appreciated. Regards, Niall.

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Quantum Ising Model
by Niall Moran 21 Sep '07

21 Sep '07

Hi all, I am trying to do some quantum Monte Carlo simulations on a simple 1D Ising model with a transverse field. I could not find any Ising model specified in the standard models.xml file. I created a file called ising_model.xml with contents listed below. Could anyone verify if this is correct as I am new to this and do not fully understand how to specify models. Kind Regards, Niall. <MODELS> <SITEBASIS name="spin"> <PARAMETER name="local_spin" default="local_S"/> <PARAMETER name="local_S" default="1/2"/> <QUANTUMNUMBER name="S" min="local_spin" max="local_spin"/> <QUANTUMNUMBER name="Sz" min="-S" max="S"/> <OPERATOR name="Splus" matrixelement="sqrt(S*(S+1)-Sz*(Sz+1))"> <CHANGE quantumnumber="Sz" change="1"/> </OPERATOR> <OPERATOR name="Sminus" matrixelement="sqrt(S*(S+1)-Sz*(Sz-1))"> <CHANGE quantumnumber="Sz" change="-1"/> </OPERATOR> <OPERATOR name="Sz" matrixelement="Sz"/> </SITEBASIS> <BASIS name="spin"> <SITEBASIS ref="spin"> <PARAMETER name="local_spin" value="local_S#"/> <PARAMETER name="local_S#" value="local_S"/> <PARAMETER name="local_S" value="1/2"/> </SITEBASIS> <CONSTRAINT quantumnumber="Sz" value="Sz_total"/> </BASIS> <SITEOPERATOR name="Sx" site="x"> 1/2*(Splus(x)+Sminus(x)) </SITEOPERATOR> <HAMILTONIAN name="ising_spin"> <PARAMETER name="h" default="0"/> <BASIS ref="spin"/> <SITETERM site="i"> <PARAMETER name="h" default="h"/> -h*Sx(i) </SITETERM> <BONDTERM source="i" target="j"> <PARAMETER name="J" default="J"/> -J*Sz(i)*Sz(j) </BONDTERM> </HAMILTONIAN> </MODELS>

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Re: [ALPS-users] Comp-phys-alps-users Digest, Vol 18, Issue 8
by GANG CHEN 20 Sep '07

20 Sep '07

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: models in classical monte carlo simulation (Matthias Troyer) > 2. Re: one question about custom measurement (Matthias Troyer) > > >---------------------------------------------------------------------- > >Message: 1 >Date: Wed, 19 Sep 2007 19:41:41 +0200 >From: Matthias Troyer <troyer(a)phys.ethz.ch> >Subject: Re: [ALPS-users] models in classical monte carlo simulation >To: comp-phys-alps-users(a)phys.ethz.ch >Message-ID: <7E292C25-4D1A-4234-82E4-BF3733ED4046(a)phys.ethz.ch> >Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed > >Hi Gang, > >The classical models cannot be as easily coded in an input file as >the discrete quantum models. We have support for classical O(N) >vector spin models with anisotropic interactions hardcoded. Which >model do you have in mind? > >Matthias > >On 19 Sep 2007, at 06:16, GANG CHEN wrote: > > > Thanks, the model is O(3) Heisenberg model with Dzyaloshinskii-Moriya anisotropy. e.g. if there are two bonds in the unit cell, each bond has different Dzyaloshinskii-Moriya vector, is it possible to deal with model? What will be the name for it in the hardcoded library? Gang >>Hi all, >> >>What is the default libary for the model in classical monte carlo >>simulation? In the tutorial there are Heisenberg model and Ising >>model which could not be found in the file lib/xml/models.xml. >>Could I define my own models as usual way? And do I refer the model >>libary in the parameter file also in the same way as >>sparsediagonalization? >> >>Thanks, >>Gang >><chggst.vcf> >> >> > > > >------------------------------ > >Message: 2 >Date: Wed, 19 Sep 2007 19:42:04 +0200 >From: Matthias Troyer <troyer(a)phys.ethz.ch> >Subject: Re: [ALPS-users] one question about custom measurement >To: comp-phys-alps-users(a)phys.ethz.ch >Message-ID: <DDDC6596-1617-436A-A232-A5E7FAB77BE9(a)phys.ethz.ch> >Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed > >You will need to code those yourself manually. We do not support such >multi-site measurements yet, but will in a future version. > >Matthias > >On 19 Sep 2007, at 02:02, GANG CHEN wrote: > > > >>Hi all, >> >>I am working on a lattice which has several sites in one unit cell. >>Let's denote site index as "i, j ,k", unit cell index as "A, B, C". >>If I want to see the behavior of some particular site in the unit >>cell, e.g. S_{A, i}; or some other local information, such as Cross >>[S_{A, i}, S_{A,j}] \dot S_{A, k}, i,j,k are three given sites in >>one unit cell, how do I define them? >> >>Thanks, >>Gang >> >><chggst.vcf> >> >> > > > >End of Comp-phys-alps-users Digest, Vol 18, Issue 8 >*************************************************** > >

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one question about custom measurement
by GANG CHEN 19 Sep '07

19 Sep '07

Hi all, I am working on a lattice which has several sites in one unit cell. Let's denote site index as "i, j ,k", unit cell index as "A, B, C". If I want to see the behavior of some particular site in the unit cell, e.g. S_{A, i}; or some other local information, such as Cross[S_{A, i}, S_{A,j}] \dot S_{A, k}, i,j,k are three given sites in one unit cell, how do I define them? Thanks, Gang

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models in classical monte carlo simulation
by GANG CHEN 19 Sep '07

19 Sep '07

Hi all, What is the default libary for the model in classical monte carlo simulation? In the tutorial there are Heisenberg model and Ising model which could not be found in the file lib/xml/models.xml. Could I define my own models as usual way? And do I refer the model libary in the parameter file also in the same way as sparsediagonalization? Thanks, Gang

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could you help look at these two definitions
by Gang Chen 18 Sep '07

18 Sep '07

Hi all, sorry to bother, I have some trouble with the parameter definition in my models Hamiltonian. Could someone help look at the "BONDTERM" and particularly the specification of parameter? In the examples in the tutorials, I saw that another set of parameters is defined in every type of bondterm, and the default values of these parameters are referred the parameters defined in the beginning. Because my model Hamiltonian is the Heisenberg's model with Dzyaloshinski-Moriya interaction, so I didn't introduce new parameters for each bond (named as J#), and simply use the parameters defined in the beginning. Can I do this? Is my definition correct? If there is something wrong in the lattice and model definition, could you help correct them? Thanks a lot. Gang

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Question about DMRG
by Justin David Peel 16 Sep '07

16 Sep '07

Hi all, I didn't get an answer when I asked before about this, but I thought that I would try again. In DMRG the common practice is to use the truncation errors at different MAXSTATES to extrapolate the energy. However, the dmrg code currently does not write out the truncation error to a file. Is there a way to have the dmrg program write this out for the last sweep? Even just one value from the last sweep or the mean would be useful. I know that the truncation error for each step is written out to the screen, but it is rather inefficient to run one batch at a time and then copy down the truncation error. I really appreciate the help that I have received thus far and am very grateful for the ALPS collaboration overall. I'd appreciate any hints you might have regarding this. Thanks, Justin Peel

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Re: [ALPS-users] ALPS
by Matthias Troyer 12 Sep '07

12 Sep '07

On 12 Sep 2007, at 18:05, Amit Choubey wrote: > Respected Sir, > > I am Amit Choubey, MSc student of IIT Kharagpur, India. I am trying > to solve Fermionic Hubbard Model using ALPS. But I am not able to > understand how should I define the creation and annhiliation > operator for fermions. Its because they follow an anticommutation > relationship and the eigenvalues are dependent on the particular > arrangement of the fermions. Please help me in this regard. An > example describing this will be really nice of you. > > Thanking You. > > Sincerely, > Amit Choubey Just look at the models.xml file in ALPS for some examples Matthias

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2 questions
by GANG CHEN 08 Sep '07

08 Sep '07

Hi, all, I have two questions to bother you. the first one is: Here is part of the model I defined. It is Heisenberg AFM model with different coupling constant J on each type of bond. See the defined BONDTERM. The default coupling Jz2 is J, and I specify J=1 in the parameter file. <HAMILTONIAN name="spin"> <PARAMETER name="Jz" default="J"/> <PARAMETER name="Jxy" default="J"/> <PARAMETER name="J" default="1"/> <BONDTERM type="2" source="i" target="j"> <PARAMETER name="Jz2" default="J"/> <PARAMETER name="Jxy2" default="J"/> Jz2*Sz(i)*Sz(j)+Jxy2*exchange_xy(i,j)+ ........ However, when I tried to run it, I got following error message. parsing task files ... Starting task 1. Cannot evaluate expression Jz2 * -0.5 * -0.5 It seems that Alps didn't take the numerical value of Jz2. Or I make a mistake somewhere. Can someone help point out? The second question about "sparse diagonalization": When I use Lanczos method to get the ground state energy, it seems that it can only give me the value of energy, not the degeneracy of states. The value of energy has error in it, as a result, sometimes, it will consider two degenerate states as two different states. Is my understanding correct? So, in order to judge whether the two states are degenerate or not from the energy value, we need to estimate of the magnitude of errors. Do you know how to do it? Run the same program several time and see the fluctuation of the corresponding energy and state? What do you suggest? best, Gang

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Comp-phys-alps-users September 2007