CLUSTER APPROXIMATION FOR THE CONTACT PROCESS

The one-dimensional contact process is analysed by a cluster approxima tion. In this approach, the hierarchy of rate equations for the densit ies of finite length empty intervals are truncated under the assumptio n that adjacent intervals are not correlated. This assumption yields a first-order phase transition from an active state to the adsorbing st ate. Despite the apparent failure of this approximation in describing the critical behaviour, our approach provides an accurate description of the steady-state properties for a significant range of desorption r ates. Moreover, the resulting critical exponents are closer to the sim ulation values in comparison with site mean-field theory.