Journal of Statistical Physics, Vol. 76, Nos. 1/2. 1994, p. 307-329.
It is known that the free energy at criticality of a finite two-dimensional system of characteristic size L has in general a term which behaves like log L as L -> oo; the coefficient of this term is universal. There are solvable models of two-dimensional classical Coulomb systems which exhibit the same finite-size correction (except for its sign) although the particle correlations are short-ranged, i.e., non-critical. Actually, the electrical potential and electrical field correlations are critical at all temperatures (as long as the Coulomb system is a conductor), as a consequence of the perfect screening property of Coulomb systems. This is why Coulomb systems have to exhibit critical finite-size effects.