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,