Systematic coarse-graining and dynamical simulations of anisotropic molecular systems: towards comprehensive modeling of organic semiconductors
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Date
2024
Authors
Nguyen, Thi Lan Huong
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Advisors
Huang, David
Kee, Tak
Kee, Tak
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Thesis
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Abstract
Organic semiconductors (OSCs) offer versatility for a wide array of applications, ranging from flexible photovoltaics and electronics to energy-efficient lighting solutions. Despite their potential, the widespread adoption of OSCs in commercial settings remains limited, often falling short in performance compared to inorganic semiconductor materials. Utilizing solution-processing methods for OSC device fabrication allows for cost-effective production and opens up avenues for innovative applications. However, challenges persist in accurately predicting behavior in solution and interfacial structures post-deposition, hindering efforts to improve device performance. Moreover, the lack of a comprehensive understanding of the fundamental physical principles governing both solution-phase dynamics and interfacial morphology adds further complexity to advancements in the field. While atomistic/fine-grained (FG) simulations provide accurate representations of molecular interactions, they are often impractical for studying OSC microstructure formation due to the prohibitively large typical domain sizes and time scales relevant to experimental conditions. Coarse-grained (CG) models offer a solution by increasing simulation efficiency through the representation of a collection of atoms as a single interacting site. In this thesis, the novel anisotropic force-matching coarse-graining (AFM-CG) theory is introduced, providing a systematic and rigorous approach for parametrizing CG models with anisotropic particles via force and torque matching. Different algorithms based on the AFM-CG theory are developed to derive accurate CG potentials for uniaxial and biaxial molecules, resulting in significant improvements in matching the structural and thermodynamic properties of realistic molecular systems compared to previous models considering anisotropy. Furthermore, an efficient and versatile pair potential for dissimilar biaxial molecules using general orientation-dependent scalar basis functions known as S-functions is introduced. This pair potential class has the ability to accurately represent a broad spectrum of molecular shapes and interactions. Through fitting pair molecular interactions for various molecules exhibiting a significant range of sizes, shapes, and interactions, the effectiveness of the biaxial S-function compared with existing anisotropic pair potentials is demonstrated. This emphasizes the suitability of biaxial S-functions for accurate modeling of OSCs. The theories and algorithms developed in this thesis will enable the accurate representation of molecular interactions in CG simulations of OSCs. This advancement will facilitate theoretical studies aimed at providing guidelines to control the microstructures and interfacial orientations of OSCs, offering valuable insights for optimizing OSC performance in optoelectronic devices.
School/Discipline
School of Earth and Environmental Sciences
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Physics, Chemistry and Earth Sciences, 2024
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This thesis is currently under embargo and not available.