Higher Order Classical Density Functional Theory for Branched Chains and Rings
We develop a general density functional theory for polyatomic molecules by taking the complete association limit of Wertheim's thermodynamic perturbation theory in a general way. By enforcing the complete association limit at an early point in the derivation and introducing the concept of molecular graphs, a general form for the free energy functional and segment densities are developed for both rigid and semiflexible molecules. The theory is applicable to branched chains, rings, or any other molecular structure. As an example the theory is applied as a second order perturbation theory to the case of molecules with a rigid three segment head and a fully flexible tail in a slit pore where bond angle of the rigid portion is an independent variable.