Dear friends, Can any body guide me how to make the program in FORTRAN77/90 or in C on square lattice for the

following quantum spin (anti-ferromagnetic) model:

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. Thanking you,

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

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