Classical Density Functional Theory for Polymers: An Open-Source Solution for Modeling Complex Fluids

Classical density functional theory (DFT) provides a robust framework for exploring and predicting the behavior of complex fluids, including weak polyelectrolytes with complex architecture, by capturing the non-ideal interactions and structural properties of these systems at the molecular level. This work presents an efficient implementation of classical DFT for polymer systems, detailing the relevant free energy functionals and computational strategies optimized for chain molecules. Through illustrative examples, we demonstrate the application of this DFT approach to various polymer physics problems, including the behavior at the interface between two polymer phases, adsorption at a surface, and the polymer-mediated interactions between surfaces. By accurately modeling the spatial distribution of polymers and their response to external fields, the method captures key phenomena relevant to weak polyelectrolyte solutions. Our results are validated against Monte Carlo and molecular dynamics simulations, highlighting DFT's advantages in computational efficiency and predictive power for large-scale and multi-component polymer systems. The presented implementation is designed for flexibility, allowing for modifications and extensions, such as incorporating field-theoretic corrections or multi-scale approaches. This framework thus provides a powerful tool for researchers aiming to understand polymeric solutions and engineer new applications in soft matter physics.