Dear Fernando Cucchietti,

Indeed the ALPS QMC applications do not support these measurements except for the Green's function sigma^plus_i sigma^minus_j in some of the codes. To answer how easy or hard it is to implement these measurements we would need to know which model you want to simulate.

Matthias

On 28 Nov 2009, at 16:05, Fernando Cucchietti wrote:

Hello all,

I am learning how to use the ALPS applications. I had reasonable success with DMRG with which I am experienced, however I was trying to study two dimensional systems with QMC and I ran into a problem: The ALPS application complains that it will not measure off-diagonal observables such as sigma_x, even less for two operators like sigma^plus_i sigma^minus_j. It measures without any problems sigma_z and correlations of sigma_z operators.

Now, my ignorance of QMC is such that I don't know if this is an intrinsic limitation of Quantum Montecarlo algorithms or just of the particular example application distributed with ALPS -- this is my first question. My second question is: if it is possible to measure e.g. sigma_x, could you give me a rough estimate of how difficult could it be to implement it with the libraries?

Thanks in advance,

Fernando Cucchietti