Correlation functions of the Ising model of solid ortho-hydrogen in the disordered phase

In a generalized molecular field approximation the time independent correlation functions as well as the time dependent ones are calculated for the Ising model of o-H₂ in the orientationally disordered phase. In our treatment the correlations fulfill their characteristic sum rule automatically. The order parameter correlation shows the characteristic singularity at the stability limit fork=0. The time dependent correlations are calculated within the Glauber stochastic model and show critical behaviour at the stability limit.