SURFACE EFFECTS ON THE SUSCEPTIBILITY OF CONFINED SYSTEMS NEAR THE CRITICAL-POINT

On the basis of the phi(4) model we describe the effect of non-periodi c boundary conditions (b.c.) on tile susceptibility or compressibility of three-dimensional (3D) confined systems for T greater than or equa l to T-c by taking into account a surface coupling. The result is comp ared with new Monte Carlo (RIG) data for the 3D Ising model with free b.c. The qualitative and quantitative differences between MC data for periodic and free b.c. are well explained by the theory. The applicabi lity of our theory to finite-size effects near the gas-liquid critical point of He-3 is briefly discussed.