QSI PhD Defense: Peng Yan

TITLE:  First-Principles and Data-Driven Design and Discovery of Two-Dimensional Layered Ferroic Materials

ABSTRACT:  Two-dimensional (2D) van der Waals (vdW) layered materials offer promising opportunities for next-generation electronic, magnetic, and ferroelectric applications. However, their discovery and rational design remain challenging due to the complex relationships among chemical composition, atomic structure, and functional properties. This dissertation integrates data-driven materials discovery, first-principles density functional theory (DFT), interface engineering, and computational automation to develop systematic approaches for identifying and designing functional 2D materials.

First, a chemistry-guided discovery strategy combining crystallographic database mining and Quantum Structural Diagrams (QSDs) is developed to identify promising layered phosphochalcogenides, narrowing approximately 930 candidate compositions to 83 unexplored materials for further investigation. To enable reliable property predictions, systematic DFT benchmarking is then performed to evaluate computational methods for layered vdW materials containing homonuclear bonds. These computational approaches are further applied to investigate electronic and magnetic properties, including the ferrimagnetic behavior of Fe₃GaTe₂ in conjunction with neutron diffraction experiments.

Building upon these foundations, the research extends toward controlling functional properties through molecular adsorption and interface engineering. First-principles calculations reveal that molecular coordination with surface Cu atoms in CuInP₂S₆ can break ferroelectric symmetry and modify polarization. Complementary studies of ferroelectric/ferromagnetic heterostructures investigate how molecular intercalation, superlattice stacking, and strain influence interfacial structure, electronic states, and ferroic behavior, providing insights into distinct mechanisms of interface control.