Hi Marcelo,
This should work, but I'm not sure if that is the gap that you want to measure, since your model does not have SU(2) symmetry. if it is the gap that you are interested in then it might be much easier and more stable to get it from a fit of the low-T susceptibility to an exponential.
Matthias
On Feb 8, 2011, at 8:47 PM, Marcelo Guimarães wrote:
Hello,
I would like to know if the parameter RESTRICT_MEASUREMENTS[Sz] works for dirloop_sse as indicated at http://alps.comp-phys.org/mediawiki/index.php/Documentation:dirloop_sse.
I'm trying to obtain the gap for (3d), H=J( S+(i)S(i+1)- + S-(i)S+(i+1) ) +D(Sz)^2 at D > Dc by calculating energy difference from E(Mz=1) , E(Mz=0) at low temperature.
Since <Sz(i)Sz(i+1)> ~ 0 , and dirloop does not measure off-diagonal correlations , I was wandering if I could use this procedure in dirloop to estimate the gap.
Thanks,
Marcelo Guimaraes.