Journal of Statistical Physics. Vol. 84, Nos. 3/4. 1996, p. 399-413.
The phase diagram and the tricritical point of a collapsing lattice animal are studied through an extended series expansion of the isothermal compressibility Kt on a square lattice. As a function of the variables of fugacity and Boltzmann weight, Kt is investigated using partial 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 tricritical fugacity x, = 0.024+/-0.005 and temperature T, = 0.54+/-0.04. Taking into account only linear scaling fields, we are also able to get the scaling exponent y = 1.4+/-0.2 and the crossover Fi = 0.66+0.08. Our results are in reasonable agreement with previous estimates in the literature.