Structure of discrete-potential fluids interacting via two piece-wise constant potentials with a hard-core

- Propose the inverse temperature method based on the power series
- Calculate the structure of two piece-wise discrete potential fluids
- An inverse temperature method is the most successful for the square-shoulder type fluid.

The structure of fluids whose molecules interact via potentials with a hard-core plus two piece-wise constant sections of different widths and heights has been studied by the perturbation theory based on the power series of an inverse temperature. The perturbation theory based on the reference system which incorporates both the repulsive and attractive potentials predicts accurate radial distribution function and direct correlation function of the discrete-potential fluids for the whole density regions. In particular, it is the most successful for the square-shoulder plus square-shoulder fluid and shifted square-shoulder fluid with a purely repulsive potential rather than the square-well plus square-well fluids with an attractive potential. It is found that the present theory predicts a more accurate structure than the rational-function approximation and conventional integral equations such as Percus-Yevick and hypernetted-chain theories in most of the cases.