Decay of correlations in fluids: The one-component plasma from Debye-Huckel to the asymptotic-high-density limit

The decay of structural correlations in the classical one-component plasma is analyzed by calculating the poles of the Fourier transform of the total (pairwise) correlation function h(r) for two integral equation theories, th e soft mean spherical approximation and the hypernetted chain (HNC). We sho w that for all except the largest values of the plasma coupling constant Ga mma, the leading-order pole contribution provides an accurate description o f h(r) at intermediate range, as well as the ultimate asymptotic decay. The crossover from monotonic decay at weak coupling to exponentially damped os cillatory decay at strong coupling is shown to arise from the same mechanis m as that which occurs for charge correlations in binary ionic fluids. We c alculate the values of Gamma at which the crossover occurs in the two theor ies. The role of higher-order poles and (within the HNC) other singularitie s in determining the intermediate range behavior of h(r) for strong couplin g is discussed. We investigate the properties of the solutions of the integ ral equations in the strong coupling, Gamma-->infinity, asymptotic high-den sity limit (AHDL). Pade approximants are employed in order to test the vali dity of the scaling laws proposed for the potential energy, direct correlat ion function, and for the poles and their contributions to h(r) in the AHDL . Our numerical results provide strong support for the validity of the theo retical predictions concerning the AHDL.