Progress in the Perturbation Approach in Fluid and Fluid-Related Theories

Significant progress made in the perturbation approach in fluid and fluid-related theories are discussed. Some of the latest advancements in perturbation theories for simple fluids were related to the λ-expansion. The free energy system was expressed as an inverse temperature expansion in one of the equations whose terms were related to fluctuations around the mean perturbation energy calculation in the reference system. Another expression was the basis of the calculation of several of the low-order perturbative terms through computer simulation. A number of researchers also derived one of the most accurate expressions for the second-order term in the free energy expansion. This approximation was found to provide better agreement with the simulation data of F2/NkT for the SW fluid.