On Mar 5, 2013, at 4:40 PM, Billa billa.j@gmail.com wrote:

Hi all,

I have been trying to set up a classical Monte Carlo simulation with a square lattice Heisenberg model. I am interested in measuring nearest neighbor correlation functions of the type <S^z _i S^z _(i+1)>. How can I define such a measurement? I saw in the ALPS DMRG tutorial that correlation measurements can be set up by inserting the MEASURE_CORRELATIONS command into the parameter file, however this does not seem to work for the Heisenberg model. How can I produce measurements of <S^z _i S^z _(i+1)> type correlators?

It should work. Please send your input files if you can't get it to work.

As a related question, where can I see how the Heisenberg model is defined in ALPS? I found definitions of the Ising, spin and various other models in the models.xml file, but there was no reference to Heisenberg.

The spin model can be used to simulate the Heisenberg model. Most of the DMRG tutorials are in fact on Heisenberg spin models.

Finally, in the tutorials on classical Monte Carlo the employed update procedure is referenced as 'cluster'. Which cluster update algorithm is used in alps precisely? I couldn't find this info in the documentation.

It uses Wolff-type cluster updates.

Thanks in advance for all replies!

Billa