### Abstract

We have developed expressions for the residual Helmholtz free energy and the residual chemical potential in terms of the correlation functions
and bridge functions in the context of the interaction-site formalism
for the Chandler-Silbey-Ladanyi equations. Unlike the corresponding
expressions for the extended-RISM equation, these expressions are
formally exact for systems described by interaction-site models.
The new expressions are similar in form to those for multicomponent
simple fluid mixtures and are found to reduce to them in the extended-atom
limit, where the bond lengths approach infinity. We have also found
that the residual Helmholtz free energy satisfies a variational principle
for a certain class of closure relations. This finding could facilitate
the development of more efficient methods for solving the Chandler-
Silbey-Ladanyi equations. We have also derived explicit expressions
for the residual Helmholtz free energy, residual chemical potential,
residual pressure, and residual internal energy in the hypernetted-chain
approximation of the Chandler- Silbey-Ladanyi equations. It is noteworthy
that the derived expressions depend solely on the correlation functions
of the system at full coupling, thus making the computation of the
various fluid properties simpler and more efficient by eliminating
the need to perform a numerical integration over a coupling constant.
We have also found that the residual Helmholtz free energy associated
with the hypernetted-chain approximation of the Chandler-Silbey-Ladanyi
equations satisfies a variational principle. Furthermore, in the
extended-atom limit, all the derived expressions associated with
the hypernetted-chain approximation of the Chandler- Silbey-Ladanyi
equations reduce to those corresponding to the multicomponent simple
fluid mixtures.

Original language | English |
---|---|

Pages (from-to) | 3002-3012 |

Number of pages | 11 |

Journal | Journal of Chemical Physics |

Volume | 100 |

Issue number | 4 |

DOIs | |

Publication status | Published - 15 Feb 1994 |

### Keywords

- rism approximation
- molecular fluids
- dielectric-constant
- potential functions
- phase-diagrams
- liquids
- water
- thermodynamics
- formalism
- diatomics

## Fingerprint Dive into the research topics of 'Proper integral equations for interaction-site fluids: Exact free-energy expressions'. Together they form a unique fingerprint.

## Cite this

Lue, L., & Blankschtein, D. (1994). Proper integral equations for interaction-site fluids: Exact free-energy expressions.

*Journal of Chemical Physics*,*100*(4), 3002-3012. https://doi.org/10.1063/1.466441