  We consider fluids where the attractive interaction at distances slightly
larger than the particle size is dominated at larger distances by a repulsive
contribution. A previous investigation of the effects of the competition
between attraction and repulsion on the liquid-vapour transition and on the
correlations is extended to the study of the stability of liquid-vapour phase
separation with respect to freezing. We find that this long-range repulsive
part of the interaction expands the region where the fluid-solid transition
preempts the liquid-vapour one, so that the critical point becomes metastable
at longer attraction ranges than those required for purely attractive
potentials. Moreover, the large density fluctuations that occur near the
liquid-vapour critical point are greatly enhanced by the competition between
attractive and repulsive forces, and encompass a much wider region than in the
attractive case. The decay of correlations for states where the compressibility
is large is governed by two characteristic lengths, and the usual
Ornstein-Zernike picture breaks down except for the very neighborhood of the
critical point, where one length reduces to the commonly adopted correlation
length, while the other one saturates at a finite value.
