The mean spherical approximation for a dipolar Yukawa fluid

The dipolar hard sphere fluid (DHSF) is a useful model of a polar fluid. Ho wever, the DHSF lacks a vapor-liquid transition due to the formation of cha in-like structures. Such chains are not characteristic of real polar fluids . A more realistic model of a polar fluid is obtained by adding a Lennard-J ones potential to the intermolecular potential. Very similar results are ob tained by adding a Yukawa potential, instead of the Lennard-Jones potential . We call this fluid the dipolar Yukawa fluid (DYF). We show that an analyt ical solution of the mean spherical approximation (MSA) can be obtained for the DYF. Thus, the DYF has many of the attractive features of the DHSF. We find that, within the MSA, the Yukawa potential modifies only the spherica lly averaged distribution function. Thus, although the thermodynamic proper ties of the DYF differ from those of the DHSF, the MSA dielectric constant of the DYF is the same as that of the DHSF. This result, and some other pre dictions, are tested by simulations and are found to be good approximations . (C) 1999 American Institute of Physics. [S0021-9606(99)50815-5].