Dear all, we are studying the AF XY model on bipartite lattice using SSE QMC. We want to see the AF long-range order in the xy plane. Thus we want to measure S^{plus}S^{minus}. We have tried to use 'MEASURE_CORRELATIONS[Offdiagonal spin correlations]' : 'Splus:Sminus', but the code gives information that this quantity can not be measured. Then we measure the Green function, which is realized in the code.

We test the Green function first using a Heisenberg model. We find the value of the Green function is always positive, and is about two times the value of S^{z}S^{z}. We guess the Green function is defined as S^{plus}S^{minus}. However the signs of the values are not consistent with a AF order. I am wondering what is the reason. We apprecieate your helps very much!

Sincerely, Huaiming Guo