USING DENSITY FUNCTIONAL THEORY TO EVALUATE APPROXIMATION METHODS FOR CHROMIUM ION-BASED 2D SYSTEMS

Abstract

In the present work, I utilize Density Functional Theory (DFT) to study three distinct chromium ion-based 2D systems. The aim of this project is to elucidate the identity and structure of the chromium ion-based monolayers achieved experimentally by my colleagues. First, I look at 2D CrS2 (of bulk space group C2/m) and 2D Cr2S3 (of bulk space group P-31c) to determine the structure of the experimental monolayer achieved after exfoliation of HxCrS2. This is done by way of geometry optimizations with different DFT approximation methods, and subsequent band structure and microscopy image simulation. In comparing my simulated data to experimental results, the selected phase of CrS2 was eliminated as a candidate for the experimental monolayer. While my Cr2S3 monolayer appears to be a promising candidate, further investigation with additional DFT calculations and approximation methods is necessary to confirm this.

Second, I examine 2D CrOCl (of bulk space group Pmmn) to determine if my lab mate has successfully exfoliated bulk CrOCl, and if the chemical structure of each layer remains the same after exfoliation. To do so, I also conduct geometry optimizations with the same DFT approximation methods as above. By comparing electron diffraction patterns to experimental results, it appears that material thickness affects diffraction signal intensity in the experimental image; nonetheless, further investigation is required to confirm if this is the case, and if CrOCl was successfully exfoliated down to the monolayer. Additionally, I simulate band structures of monolayer CrOCl; looking ahead, DFT analysis with a hybrid approximation method will prove useful to further evaluate the band gap of this 2D material.