Relations among the modern theories of diffusion-influenced reactions. I. Reduced distribution function theory versus memory function theory of Yang,Lee, and Shin

It is shown that exactly the same results of the memory function theory of diffusion-influenced reactions, presented by Yang, Lee, and Shin, can be de rived from the nonequilibrium reduced distribution function (RDF) theory. I nstead of the usual dynamic superposition approximation (SA), which has bee n widely used to truncate the hierarchy of RDF evolution equations, we intr oduce another type of truncation approximation. The new approximation provi des simple analytic solutions that are in better agreement with the compute r simulation and the known exact results than those obtained with the SA. ( C) 1999 American Institute of Physics. [S0021-9606(99)51746-7].