Wave vector dependent susceptibility of kd2po4 in the four cluster approximation

The self consistent four cluster approximation for the short range Ising model is extended to calculate the finite wave vector (q) dependent susceptibility. The results explain quantitatively the strong anisotropy found in inelastic neutron scattering in KD^PO^. The ice rule limit of the above model produces a singularity in the scattering intensity, as q ->0, which is similar to that resulting from a long range dipolar force.