May 2007 - Comp-phys-alps-users - lists.phys.ethz.ch

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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ALPS 1.3b4 released
by Matthias Troyer 30 Jun '07

30 Jun '07

I have put the current ALPS version (1.3b4) on the web. Before the final release there are only a few things that need to be fixed: * correct structure factors for non-square and non-cubic lattices * add evaluation of custom measurements to fulldiag * finalize the documentation Best regards Matthias

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Re: [ALPS-users] Some questions on ALPS
by Synge Todo 31 May '07

31 May '07

Dear Dr. Chern, Cc: comp-phys-alps-users From: "CHERN, Chyh-Hong" <chern(a)issp.u-tokyo.ac.jp> Date: Wed, 30 May 2007 13:58:20 +0900 > Dear Professor Todo, > > Sorry for occupying your valuable time. We encounter some problems when > using your ALPS. We will appreciate highly if you can kindly help. > > I am a postdoctoral researcher in Oshikawa's group in ISSP. Recently, we > are interested in the transverse Ising model in the kagome system. We are > doing the Monte Carlo simulation and would like use your exact > diagonalization in ALPS to calibrate. I attached the lattice.xml and parm1 > that I used. We doubt on the results and would like to listen to your > comments. Let me list what happened to us. > > 1. We obtained the exactly the same results for L=1 and L=2 on energy, > entropy, specific heat, and the free energy. When running L=3, we failed to > get any results even though the memory is only used ~ 25%. Your kagome lattice with L=3 has 27 vertices, which obviously requires too much amount of memory (8*(2^27)^2 bytes = 10^8 GB!) to store the full Hamiltonian matrix... Instead of the fulldiag code, you can use my qmc code (qmc/looper), as long as the diagonal (Sz) interaction is ferromagnetic (i.e. no frustration). > 2. If we do not add CONSERVED_QUANTNUMBERS="Sz" in the parm1, we do not have > the result on the susceptibility but do have others. If we do include that > line, we have susceptibility, but lose the results on other thermodynamics > quantities. As we know, Sz is not the conserved quantum number for the > Ising model in the transverse magnetic field. Calculating canonical correlations of the operators which do not commute with the Hamiltonian requires substantial CPU time (N^3?). This is the reason why the fulldiag skips measuring the susceptibility unless total Sz is a conserved quantity. Again you can use qmc/loop, which calculates the susceptibility even in this case, instead for calibrating your simulation code. Best regards, Synge

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how to modify spin model in models.xml file
by aniket＠jncasr.ac.in 10 May '07

10 May '07

Hi, I am in the very early stages of experimenting around with ALPS. I have special interest in quantum Monte Carlo. I want to modify spin model(models.xml file) in such manner that I can give different spin values to different lattice points. I have attached unit cell of Kagome lattice(kagome1.pdf). In that point C, are having same spin value (i.e 1) whereas, points D and E are having spin value 2. Please tell me the procedure which incorporates this change. with Regards, Aniket

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ALPS release 1.3b5
by Matthias Troyer 02 May '07

02 May '07

Release 1.3b5 of ALPS is ready for download. It contains a bugfix for fermionic simulations with the new DMRG application, as well a a fix to the momentum iterations for structure factor measurements on non- square or non-cubic lattices. Matthias

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