July 2008 - Comp-phys-alps-users

Re: [ALPS-users] correlation function+susceptibility
by Fritz Koermann 12 Aug '08

12 Aug '08

Dear Prof. Matthias Troyer, many thanks for your answer :)! > Do you want to measure the real-space correlation function or is the > magnetic susceptibility as an integrated measure enough? We would like to measure the real-space correlation function in order to separate between short- and long-range interactions and their influence on the internal energy. Is it possible to measure such a function using alps? I have two more minor questions concerning the output: Is the susceptibility \chi given out by alps equivalent to \chi=\beta*(<m^2>-<m>^2)? Is it possible to make a snapshot (spin position+spin alignment) of the spin system at a certain time-step? Again many, many thanks for your support. Best regards, Fritz Koermann --- Max-Planck-Institut für Eisenforschung GmbH Max-Planck-Straße 1 D-40237 Düsseldorf Handelsregister B 2533 Amtsgericht Düsseldorf Geschäftsführung Prof. Dr. Jörg Neugebauer Prof. Dr. Anke R. Pyzalla Prof. Dr. Dierk Raabe Prof. Dr. Martin Stratmann Dipl.-Kfm. Herbert Wilk Ust.-Id.-Nr.: DE 11 93 58 514 Steuernummer: 105 5891 1000 -------------------------------------------------

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ALPS group on LinkedIn
by Matthias Troyer 27 Jul '08

27 Jul '08

Dear ALPS users and developers, I have created an ALPS group on the LinkedIn IT-networking site. Feel free to join using the link http://www.linkedin.com/e/gis/144124/5E1E716924F5 Matthias

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question about spin susceptibility
by Gang Chen 27 Jul '08

27 Jul '08

Hi All, Sorry to bother, I have a question about spin susceptibility. In my problem, the total spin is not a good quantum number. If I apply exact diagonalization code, how do I obtain spin susceptibility? One thing you might suggest is to measure total spin Sz (say the applied magnetic field is along z direction), and calculate \chi approximated as (<S_z>_h - <S_z>_{h=0}) /h. Then how to ask ALPS to measure <S_z>? Same question for quantum monte carlo. Could anyone be kind to offer a help? Thanks, -- GANG CHEN Department of Physics U.C. Santa Barbara

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ALPS release 1.3.3
by Matthias Troyer 26 Jul '08

26 Jul '08

Dear ALPS users and developers, Release 1.3.3 has been posted including * a bug fix for correlation measurements in DMRG when using periodic boundary conditions. Note however that it is recommended to use DMRG with open boundary conditions. * separate measurements of energies for the individual bond types in spinmc * minor improvements to models.xml Matthias Troyer

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ALPS dmrg running and output question
by Kaden Hazzard 25 Jul '08

25 Jul '08

Hi, We have recently installed the ALPS code, downloaded from the links on the Wiki. We are using version 1.3.2 of the libraries and applications. The install went smoothly, and the tests worked fine. We have both Cygwin and Ubuntu installs and the problems. We successfully ran some spin models with qmc, dmrg, and exact diagonalization. However, we attempted to run some DMRG calculations with a fermion Hubbard model, and this was unsuccesful. We used a periodic boundary condition chain lattice and a non-interacting system to start with, and use the default "models.xml" and "lattices.xml" that came with the packages. Our input file was ---- BEGIN INPUT FILE, parm-fermion.xml ---- LATTICE="chain lattice" SWEEPS=4 MAXSTATES=26 CONSERVED_QUANTUMNUMBERS="Nup,Ndown" { MODEL="fermion Hubbard", L=10, Nup_total=1, Ndown_total=1 mu=1.0 t=1.0 U=0 NUMBER_EIGENVALUES=1 MEASURE_LOCAL[local spin up density]=n_up MEASURE_CORRELATIONS[up up Green function]="cdag_up:c_up" MEASURE_CORRELATIONS[up down Green function]="cdag_up:c_down" MEASURE_CORRELATIONS[down down Green function]="cdag_down:c_down" MEASURE_CORRELATIONS[up density up density correlation function]=n_up MEASURE_CORRELATIONS[down density down density correlation function]=n_down MEASURE_CORRELATIONS[up density down density correlation function]="n_up:n_down" } ---- END INPUT FILE ---- When we run this ("parameter2xml parm-fermion" then "dmrg parm-fermion.in.xml"), though the energy appears to be correct, we (1) obtain correlation functions which are completely different than the expected result (often coming out to be zero) and (2) most of the site-to-site correlations (e.g., site i to site j, with i not equal to zero) are missing. A symptom may be provided by the (stderr?) output of the code: "Did not get the right number of measurements". The problem is independent of the SWEEPS and MAXSTATES used. If we run the exact diagonalization code "sparsediag", however, we obtain the expected results. So it seems we are setting up something incorrectly with the dmrg input. To further examine the problem, we re-ran with open boundary conditions (just changing "chain lattice" into "open chain lattice" in the file above). Although now the right number of measurements appear to be taken and the right correlation function elements are non-zero, the results still disagree with our expectations and exact diagonalization. Finally, we obtain similar problems with bosons. Spin models, however, work without problem and agree with exact diagonalization. We have not included the output files since they are somewhat lengthy and should be reproducible, but if it would help we would be happy to send them. Thanks for any help and the wonderful program! Kaden and Stefan

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(no subject)
by Fritz Koermann 18 Jul '08

18 Jul '08

Dear Prof. Matthias Troyer, I would like to investigate the local magnetic order and its contribution to the internal energy for the classical ferromagnetic 3D Heisenberg model above the critical temperature. Is it possible to define therefore some correlation function in alps or are they eventually already defined? Is it possible to link the mean 'cluster size' output to the local magnetic order (when using cluster updates within the classical MC)? Since I'm a newbie in the MC, let me ask: there is a finite contribution to the internal energy above the critical temperature, is this only due to the finite tail of the (total) magnetization or is this due to local order, still existing in the system above Tc? Many, many thanks for your help :), best, Fritz --- Max-Planck-Institut für Eisenforschung GmbH Max-Planck-Straße 1 D-40237 Düsseldorf Handelsregister B 2533 Amtsgericht Düsseldorf Geschäftsführung Prof. Dr. Jörg Neugebauer Prof. Dr. Anke R. Pyzalla Prof. Dr. Dierk Raabe Prof. Dr. Martin Stratmann Dipl.-Kfm. Herbert Wilk Ust.-Id.-Nr.: DE 11 93 58 514 Steuernummer: 105 5891 1000 -------------------------------------------------

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ferromagnetic interaction
by Brian Keith 09 Jul '08

09 Jul '08

Hello professor Troyer, I am trying to use ALPS to study a magnetic heisenberg ladder with anti-fm interactions in the rail direction and ferromagnetic interactions in the rung direction. I believed it would be easy to simulate if I set J_rung= 1 and J_rail= -1 but I get the same MvT results whether I do it this way or make it a uniform ladder. Is changing the sign the correct way to simulate ferromagnetic interactions? thanks for your help, Brian

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