COLLAPSE TRANSITION OF A 2-DIMENSIONAL LATTICE ANIMAL

The phase diagram and the tricritical point of a collapsing lattice an imal are studied through an extended series expansion of the isotherma l compressibility K-T on a square lattice. As a function of the variab les of fugacity and Boltzmann weight, K-T is investigated using partia l differential approximant techniques. The characteristic flow pattern of partial differential approximant trajectories is determined for a stable fixed point. We obtain satisfactory estimates for the tricritic al fugacity x(1) = 0.024+/-0.005 and temperature T-t = 0.54+/-0.04. Ta king into account only linear scaling fields, we are also able to get the scaling exponent gamma = 1.4+/-0.2 and the crossover phi = 0.66+/- 0.08. Our results are in reasonable agreement with previous estimates in the literature.