Abstract
We examine two central features of two well-known integral equations for interaction site fluids: ~i! the Chandler?Silbey?Ladanyi equations,
and ~ii! the site?site Ornstein?Zernike equation. The first feature
involves the influence of connectivity constraints. Specifically,
we identify the restrictions imposed on the site?site correlation
functions arising from the constraints of connectivity between sites
within a molecule. We find that when the Chandler?Silbey?Ladanyi
~CSL! equations, a set of diagrammatically proper integral equations,
are combined with a general approximate closure, they do not necessarily
satisfy these connectivity constraints. On the other hand, the site?site
Ornstein? Zernike ~SSOZ! equation, combined with a simple fluid closure,
does satisfy these constraints. These findings profoundly affect
the long-range behavior of the correlation functions and the dielectric
constant of the bulk fluid. These findings are also important for
the development of computational methods to obtain accurate numerical
solutions of the CSL and SSOZ equations. When theories do not satisfy
the above-mentioned connectivity constraints, we find that the resulting
correlation functions do not satisfy the local neutrality constraints,
which is a necessary requirement for any theory to properly predict
the fluid dielectric constant. Instead, the correlation functions
satisfy the constraints applicable to ionic fluids, that is, the
Stillinger?Lovett moment conditions. This leads to the prediction
of an infinite fluid dielectric constant. The second feature which
we examine involves the influence of auxiliary sites on the prediction
of the site?site total correlation functions.We prove that the addition
of certain types of auxiliary sites does not affect the correlations
between real sites when the Chandler?Silbey?Ladanyi equations are
combined with a general approximate closure. The predictions of the
SSOZ equation, combined with a general approximate closure, have
been shown to depend on the presence of auxiliary sites. However,
in the case of the Percus?Yevick closure for systems characterized
by hard-sphere interaction sites, we are able to prove that the SSOZ
equation does not exhibit this dependence for certain types of auxiliary
sites.
Original language | English |
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Pages (from-to) | 5460-5470 |
Number of pages | 11 |
Journal | Journal of Chemical Physics |
Volume | 102 |
Issue number | 13 |
DOIs | |
Publication status | Published - 1 Apr 1995 |
Keywords
- molecular fluids
- dielectric-constant
- rism approximation
- dipolar diatomics
- phase-diagrams
- thermodynamics
- solvation
- formalism
- liquids