Applied Science Events
[PAST EVENT] Dissertation Defense - Yiqi Yang
Yiqi Yang, "Exploring Electron Correlation Effects in Two-dimensional Models and Materials: A Quantum Monte Carlo Study" Zoom Link Available Upon Request
Abstract:
Electron correlations are central to complex quantum phenomena. This dissertation explores ground-state electron correlations in two-dimensional (2D) models and real materials. The 2D homogeneous electron gas (HEG) is a fundamental model that provides exchange-correlation energies essential for density functional theory (DFT). It is also directly relevant to experimental studies of 2D materials. In many experiments, metallic gates screen the Coulomb interaction between electrons. We build a density functional from 2D HEG under gate screening. This enables efficient DFT calculations that incorporate gate screening effects. We also examine how gate screening alters ground-state properties of the 2D HEG, providing insights to experiments on 2D materials. In parallel, we study the 2D Hubbard model, another fundamental model in strongly correlated systems. It has been extensively studied owing to its simple form, rich phase diagram, and relevance to high-temperature superconductivity. To evaluate its response properties with constraint-path auxiliary-field quantum Monte Carlo (CP-AFQMC), we typically add a relevant perturbation and compute the energy derivative with respect to the perturbation strength by finite difference. We developed a branching random walk with correlated sampling that allows CP-AFQMC calculation on derivatives with finite difference more efficiently. Finally, we help in assessing the accuracy of other methods by applying auxiliary-field quantum Monte Carlo to systems where it can generate numerically exact results.
Bio:
Yiqi Yang was born in Pingxiang, Jiangxi, China. He earned his bachelor's degree from Zhengzhou University in 2019 and subsequently joined Prof. Shiwei Zhang's research group at William & Mary, studying quantum many-body physics numerically. After graduation, Yiqi will begin a postdoctoral position at Lund University in Sweden, continuing his research in quantum many-body physics.
Sponsored by: Physics