[gmx-users] interaction parameter-polymer solution system

Moeed lecielll at googlemail.com
Mon May 17 15:26:51 CEST 2010

Dear experts,

I am interested in calculation of Flory interaction parameter for ternary
system of polyethylene/n-Hexane/ethylene.

Flory-Huggins lattice theory for polymer solvent systems defines interaction
parameter (binary) in terms of interaction energies between lattice sites.

binary interaction parameter  =z*delta (e)/RT

z=coordination NO. which is the number of neighbors in a lattice site
delta e=e12 -(e11+e22)/2       : net change in interaction energies upon
mixing (polymer: polyethylene in solvent :hexane)

e12 [kcal/mol] is the interaction energy between polymer and solvent (of
course after mixing)
e11, e22 interaction energy between identical molecules before mixing
(polymer or solvent)

Since we are talking about energies between lattice sites my interpretation
is that only non bonded interactions should be considered among all energy
terms.(vdw and electrostatics).

1- However, I dont know if I need to include electrostatics terms since the
system is apolar (only hydrocarbons). Also, do LJ energy figures (or
coulomb) given by g_energy refer to e11,e22.. interaction energies?

2- To calculate these interaction energies, for instance for identical
molecules , Hexane,  how many molecules i need to put in a simulation box.

3- Do I need to consider "free energy of solvation" for this type of

Many thanks,
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