From ab initio to downfolded lattice models: Exploring charge density wave physics

Abstract

This dissertation explores downfolded models in condensed matter physics, emphasizing their role in understanding the interplay between electronic and lattice degrees of freedom, particularly within the low-energy domain. The research demonstrates that downfolded lattice models accurately reproduce Born-Oppenheimer potential energy surfaces of ab initio methods, while offering computational speedups of multiple orders of magnitude. This enables extensive molecular dynamics simulations and insights into charge density wave physics in real materials. Through collaborations between experiment and theory, the work challenges the understanding of conventional charge density wave physics by revealing nonlinear mode-mode coupling in materials like monolayer 1T-VS2 . It also confirms the existence of a charge density wave with unconventional electronic gap features in monolayer 1H-NbS2. Furthermore, it demonstrates how molecular dynamics simulations can be employed to determine the transition temperature of the charge density wave phase transition in monolayer 1H-TaS2 . In summary, this research advances charge density wave physics through interdisciplinary collaboration, while providing downfolded lattice models as a valuable tool for understanding dynamics and thermodynamics for systems beyond the charge density wave phenomenon. It opens avenues for exploring phase transitions, correlations, and quantum phenomena, showcasing the transformative potential of downfolded lattice models.