Interfacial probe at elemental selectivity is highly sought after experimental tool. Chemical phenomena happen at the interface and our understanding these processes is often challenging. Second harmonic generation (SHG) spectroscopy technique can selectively probe the interface due to symmetry breaking. Coupling this technique with core electron XUV/X-ray spectroscopy allows elemental selectivity. In this regard, the development of novel core level second harmonic generation spectroscopy demonstrates a powerful tool at atomic resolution. Theoretical framework for simulation of XUV/X-ray SHG is developed to study different interfaces and interpret the experimental result. In this research, we explored Li ion displacement in ferroelectric perovskite LiOsO3 is studied via XUV-SHG, boron electronics structure at inorganic/organic junction and Li mobility in solid-state electrolyte lithium lanthanum titanate. In all cases, the bulk responses were indistinguishable between different interfaces while the surface sensitive SHG technique demonstrate different responses. Our approach shows a promising result toward elemental selective interfacial probe.

Most scenarios in our daily life can be related to thermodynamic principles. The investigation of thermodynamic phenomena, including heat transfer, chemical reactions, and dynamics, are explored to develop various appliances that play a fundamental role in our current lives. Therefore, thermodynamics are the foundation of our modern life framework.

However, it is impractical to “manually” put all thermodynamic theories together to predict the outcomes. Therefore, computer simulations have been developed to simulate those complicated models for practical applications. In this research study, we used computer simulations with core thermodynamic disciplines to resolve the challenges encountered in the industry and also the threat from climate change. With the lab collaboration, this work provided not only the theoretical consequences but also the experimental supports in practical uses.

Along with the computational and experimental bases, we explored the fields on generating the appropriate forcefield models, investigating the materials characteristics inside the Metal-Organic frameworks, and analyzing the curvature-selective ligand adsorption toward nanoparticles. Considerations of larger systems applied in real life are a natural extension, and insights on the behavior of theoretical functions are being explored.

Dynamic Mechanical Analysis (DMA) is an important experimental characterization technique for the mechanical properties of polymers. In this paper, we translate such a technique into a Molecular Dynamics (MD) simulation workflow capable of outputting properties from DMA within a much wider frequency and temperature range than what can be experimentally observed. We also introduce metrics for convergence of simulation runtime and DMA straining size that are not discussed in comparable computational literature but that drastically affect the accuracy of results. We validate the efficacy of the work by comparing our obtained storage and loss modulus data on Polyvinylidene Fluoride (PVDF) with previous computational literature and indicating performance and accuracy improvements for such study based on our convergence metrics. Finally, we perform a complete workflow run at GHz-range frequencies on PVDF utilizing the All-Atom Optimized Potential for Liquid Simulations (OPLS-AA). With this, we hope to validate and justify this forcefield as a good standard for high-throughput analyses on other polymers with the workflow and to compare our data with experimental results employing the Time-Temperature Superposition (TTS) method.

The advancement of heterogeneous catalysis and electrocatalysis is essential for developing new energy conversion and storage technologies. Traditionally, heterogeneous catalysis design has focused on engineering the interaction of surface sites in a steady-state model to achieve a "just-right" binding strength to the adsorbate. Recent models predict that dynamically controlling the binding energy of catalytic sites to reaction intermediates can result in per-site activities that outperform previous steady-state catalysis models. Ferroelectric nanomaterials offer a unique opportunity for dynamic catalysis as they can present two distinct chemical surfaces depending on their polarization direction adding an additional dimension to control the interaction of adsorbates with the catalytic surface.This thesis is an effort to design, model and investigate ferroelectric perovskites and their implications in the new paradigm of dynamic electrocatalysis. To achieve this a combination of ab-initio DFT calculations, synchrotron-based spectroscopy and electrochemical measurement were employed to investigate the role of ferroelectric polarization in perovskite thin films grown by molecular beam epitaxy. First the role of polarization switching on the surface structure of bare BaTiO3 ferroelectric thin films and their implications toward hydrogen evolution reaction as a model reaction has been stablished. Next, a combination of computational spectroscopy based on many-body electron excitations and synchrotron scanning tunneling microscopy was used to investigate the role of polarization switching on X-Ray absorption of BaTiO3 and its O2 adsorption activity. After stablishing the role of ferroelectric switching on the surface chemistry an electronic structure of bare thin films, a complex heterostructures consisting of a ferroelectric BaTiO3 layer and an atomically thin SrRuO3 layer acting as catalytic skin was constructed. It was shown that this model exhibits ~3 times higher catalytic activity for hydrogen evolution reaction in dynamic mode compared with steady-state conditions. Coupling dynamics with intrinsic properties of exotic materials such as ferroelectrics to control the interaction of intermediates over a single catalytic surface as demonstrated here can offer a wide array of enhancements in catalysis beyond traditional steady-state models.

π-Conjugated polymers are an emerging class of materials for use in solar cells, transis-tors, LEDs, and sensors. Both the electronic and thermomechanical properties of π-conjugated polymers are governed by the fundamental rigidity of the polymer backbone. For example, we find that two highly similar compounds have radically different thermomechanical and electronic properties with only a small change in backbone structure. It would be advantageous to be able to characterize this property for use in designing novel polymeric compounds. One method to do this would be computational techniques, particularly molecular dynamics (MD). However, MD simulations of π-conjugated polymers are often highly distorted due to nonbonded interactions, particularly steric interactions. This dissertation describes a universal method to use computa- tionally chemically modified π-conjugated polymers to isolate the fundamental energy governing polymer rigidity. Not only does this method result in MD simulations that are significantly more accurate, it additionally allows for simple understanding of the underlying fundamental forces governing π-conjugated polymers. This improved understanding can lead to the use of this fundamental property in physical-organic chemistry experiments. Additionally, isolation of the fundamental energy governing π-conjugated polymer rigidity opened avenues to study effects that previous were entirely subsumed by nonbonded interactions. A novel type of torsion in π- conjugated polymers was characterized using this technique, resulting in yet another increase in accuracy in MD modeling of π-conjugated polymers. Additionally, the models show that this may be a significant source of torsion in the popular class of donor-acceptor polymers. An additional method was developed to quickly characterize the coupled styles of torsion in conjugated poly- mers. Finally, the method was used to correct for long-range interactions between monomers in π-conjugated polymers, resulting in a moderate increase in accuracy. These studies for the first time additionally allowed comparison of short-range and long-range rigidity in π-conjugated polymers. Overall, this work allows for characterization of the fundamental property governing π-conjugated polymers for rational design.