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A Hybrid Density Functional Theory for Solvation and Solvent-Mediated Interactions

  • Author(s): Jin, Zhehui
  • Advisor(s): Wu, Jianzhong
  • et al.

Recent years have witnessed a renewed interest in statistical mechanics of solvation directed toward a better understanding of hydration and water-mediated interactions from a molecular perspective. A good understanding of aqueous solvation is essential not only in solution thermodynamics but also for studying functions and interfacial properties of nanostructured materials in a solution environment. Such knowledge is also indispensable for understanding biological processes in vivo and in vitro.

While conventional theories of solvation are mostly based on a continuous representation of the solvent, due to the lack of fundamental understanding of the properties of solvent molecules near solute surface, the materials fabrication and self-assembly of functional biomacromolecules often rely on costly and time-consuming "trial-and-error" approaches. The objective of this Ph.D. research is to provide a theoretical framework for efficient investigation of the microscopic structure and thermodynamic properties of flexible and rigid molecules in solution through a unified density functional theory (DFT) and a hybrid method incorporating molecular simulations. Toward that end, I have applied the DFT to the study of the microscopic structure and thermodynamic properties of polymers and polyelectrolytes in in confined geometry. I have tested the numerical performance of the DFT with molecular simulations and scaling analysis and examined the effects of packing densities, the curvature of confinement, the degree of polymerization, the salt concentration and valence on the properties and microscopic structure of confined polymers and polyelectrolytes. In addition, I developed a hybrid method combining the molecular simulations and used the DFT to study the microscopic structure and thermodynamic properties of complex systems. While molecular simulation can provide the microscopic structure, the DFT can connect the microscopic structure to the thermodynamic properties through accurate free energy functional. This efficient hybrid method was extend to the study of colloidal interactions and potential of mean force underlying "lock-and-key" interactions in a solution environment and to ion solvation in water. The numerical performance of hybrid method is very good comparing to molecular simulations, while the new method drastically reduces the calculation time. Furthermore, I studied the solvent distribution and behavior near a solute ranging from microscopic to macroscopic scales, which is closely related to the understanding of hydrophobic phenomena and fabrication of superhydrophobic materials. Lastly, the solvation free energy of nanoparticles and the shape effect on the nanoparticle solvation were investigated through morphological thermodynamic with negligible computational costs.

Accomplishments from this work contribute toward a better understanding of solvation and solvent-mediated interactions in complicated molecular systems and will have broad impacts on both fundamental research and engineering applications.

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