[ALPS-users] Space-dependent terms

Hi, I have another question, I would like to include a term in the hamiltonian to be solved in a 2D 4x4 square lattice of the form H_s= -alpha * (x_i y_j - x_j y_i) where the x and y reflect the position of the nearest neighbors, i=(x_i,y_i) and j=(x_j,y_j). I was thinking to use a term in the model definition like <BONDTERM type="1" source="i" target="j"> -alpha*(x(i)*y(j)-x(j)*y(i))) </BONDTERM> Is this correct or I need to define x and y and modify the lattice somewhere?. Thanks in advance. J. Vijande University of Valencia.