Facing Complex Soft Matter: Tools, Validation, and Case Studies

Doctoral thesis, 2024

We face a complex soft matter challenge where ab-initio theory can offer unique insight. The behavior of soft matter reflects the competition between intricate intermolecular interactions and subtle energy balances. Most of those problems are complex, that is, we lack complete experimental characterizations. In fact, empirical characterization of these systems are difficult because the systems can easily change under external stimuli.
This status is a challenge for traditional material theory that normally relies on at least some measurement input: with complex soft matter we must start by making plausible predictions for the structure that may have multiple relevant phases.

This thesis develops computational tools and methods capable of predicting and analyzing the behavior of complex soft matter. We advance the application of Density Functional Theory through the development of new computational tools, notably a range-separated hybrid van der Waals Density Functional (vdW-DF) called AHCX. AHCX integrates non-local correlation and exchange mechanisms, demonstrating enhanced accuracy and transferability across various problems, from thermophysical properties in bulk materials to molecular and adsorbate systems. Additionally, this thesis work documents the implementation of the vdW-DF spin-stress tensor in \textsc{Quantum ESPRESSO}, enabling efficient predictions of spin-polarized systems and magnetic properties.

We apply AHCX, and the latest range-separated hybrid vdW-DF termed AHBR, to characterize the activation of oxygen in complex catalytic systems such as Cu-Chabazite zeolites and enzymatic crystals. We prove the utility of these functionals in accurately modeling both chemical and physical binding without empirical adjustments.

Finally, I introduce our methods and tools to study the properties of orthorhombic phases of polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF).
We contrast these with those of polyethylene (PE) using the related vdW-DF-cx functional. Unlike PVDF and PE, PVF lacks a definitive experimental consensus on its structure, and is an example of a complex soft-matter problem. We validate vdW-DF-cx's accuracy with PE and PVDF and extend our analysis to the PVF system, allowing for the impact of thermal excitations. This investigation furthermore predicts PVF's mechanical behavior, polarization response, and plastic deformation.

In summary, the thesis seeks to enhance the understanding of complex soft matter and improve theoretical tools for predicting their behavior.