Yet, another variant (SAFT-VR) using attractive potentials of variable range was
developed by Gill-Villegas et. al. [75]. Thefreeenergyandradialdistributionfunction
for the attractive reference (spherical) fluid are obtained using a high temperature
expansion up to the second order. The resulting EOS was analyzed for different at-
tractive potentials such as SW or Yukawa with variable ranges given by the parameter
λ. However, this includes an additional parameter to be fitted.
The strength of these different variants of SAFT depends upon the way chain
connectivity is included into the attraction term. Chain connectivity reduces both re-
pulsive and attractive Intermolecular interactions between the segments of the chains
as compared to a system of unbonded spheres. This chain connectivity effect which is
due to the shielding of chain segments by other segments of the same chain depends on
system density as well as on chain length. Both mean field and HR-SAFT dispersion
term do not account for chain connectivity, only the hard chain (or repulsive) term
includes chain connectivity. Other variants such as LJ-SAFT, soft-SAFT, SAFT-VR,
etc. include chain connectivity in both the repulsive and attractive interactions by
bonding a reference fluid which includes attractive interactions. The properties of
these attractive reference (spherical) fluids are obtained again by applying a pertur-
bation to the hard sphere reference fluid. For example, Barker and Henderson [76, 77]
perturbation theory can be used to obtain the properties of SW or LJ spherical fluid
using the reference hard sphere fluid. On the contrary, Gross and Sadowki [78] fol-
lowed a different approach to first form the hard chain molecules using SAFT-HS and
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