Modified Benedict–Webb–Rubin Equation of State for the Modified Lennard-Jones Fluid

Abstract

We have proposed a modified Lennard-Jones (mLJ) potential to deal with problems, such as the accurate determination of the melting condition, in which an attractive interaction plays an essential role, but its range need not necessarily extend to infinity. An accurate phase diagram, including the triple and the critical points of the system characterized by the mLJ potential, has been investigated using mainly thermodynamic integration. To predict the thermodynamic behavior of the system, it is further desired to construct the equation of state (EOS) as accurately as possible. The modified Benedict–Webb–Rubin EOS was employed to this end. The 33 parameters involved in the equation were carefully determined in order for the EOS to be compatible with the temperature dependences of the virial coefficients as well as with an extremely large set of thermodynamic data obtained from our own molecular dynamics simulation performed over a wide fluid region. The resultant EOS was found to be not only sufficiently accurate at temperatures up to twenty times as high as the critical-point temperature but also effective in practical use.