Graduation Year

2022

Date of Submission

4-2022

Document Type

Campus Only Senior Thesis

Degree Name

Bachelor of Arts

Department

Physics

Reader 1

Sahar Sharifzadeh

Reader 2

Kevin Setter

Abstract

We studied the electron-phonon interactions in insulating 2-D materials, specifically MgI2, SnF4, and Ag2Br2, from the first principles. We calculated the band-gap renormalization of stoichiometric MgI2 and SnF4 arising from electron-phonon interactions. We perform Density Functional Theory(DFT), Density Functional Perturbation Theory(DFPT), and the Special Displacement Method(SDM) calculations. The vibrational properties of MgI2, SnF4, and Ag2Br2 were analyzed under DFPT to calculate the phonon dispersion plots of the materials. We aim to provide reference results of the methodology used here, which colleagues will then use for an automated workflow. A secondary goal of this project is to gain a deeper under-standing of electronic structure theory and computational tools used to perform analysis on 2-D materials. In 2D materials, we expect electron-phonon interactions to be strong because of the weak screening in low dimensions, and so we need to understand how they impact the electronic properties. MgI2 behaves according to the study conducted by Mounet and colleagues[14], but SnF4 does not. In the case of SnF4, we found out that there is symmetry breaking due to the presence of phonons, and therefore the interactions are not perturbative. To run Zero-Point Renormalization calculations on SnF4 and Ag2Br2, we decided to displace the supercell of the respective materials along the negative phonon modes in the Brillouin zone and get a theoretically more stable structure for the supercell. This research project is a mix of physics, chemistry, and computational physics.

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