Dear all, I am using ALPS software for exact diagonalization. There is much examples for writing models like Heisenberg, t-J, Hubbard etc. I have a difficulty to write a complicated Hamiltonian. For example, if I want to write "model.xml" for Hamiltonian :

H = J*nnsum(i,j)*S_{i}*S_{j} +

J'*sum(i)*sum(delx)*sum(dely)*[(S_{i}*S_{i+delx})*(S_{i+delx+dely}*S_{i+2*delx+dely})]

First term is simply Heisenberg term and second is another type coupling term. How can the second term be written in xml format. Thanking you,

With Best regards Rakesh Kumar School of Physical Sciences, JNU, New Delhi-110067 (INDIA) Mob.No.: +91-9891397108

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