Doctoral Dissertations

Keywords and Phrases

Crystal structure prediction; First-principles calculations; Metal chalcogenides

Abstract

A novel crystal structure prediction (CSP) method has been developed to predict energetically favorable (stable) structures based on targeted chemical compositions. It leverages the structural characteristics of recurring motifs featured in many crystals and symmetry restrictions from space groups to effectively lower the degrees of freedom of a system when conducting CSP simulations. The proposed method is applied to predicting low-energy structures of two metal chalcogenide systems: Li3PS4 and Na6Ge2Se6. Both systems feature rigid bodies in their structures as building blocks, making them particularly suited to the proposed method. The validity and effectiveness of this method are demonstrated by not only identifying the experimentally observed phases for both chemical compositions but also predicting a novel Na6Ge2Se6 phase that possesses much lower energy than the currently known lowest energy phase, as evaluated through first-principles calculations. This predicted Na6Ge2Se6 phase is then directly compared to the observed one in terms of structural, elastic, electronic, phonon, thermal, and optical properties. The results display differences and similarities across every aspect as well as showing the mechanical and dynamic stability of the predicted Na6Ge2Se6 phase and a lower free energy at elevated temperatures than its observed counterpart. The method is then extended to quaternary systems: LiZnPS4 and LiMnPS4. The lowest energy structure identified through CSP simulations for LiZnPS4 coincides with the synthesized phase. For LiMnPS4, an even lower energy phase is predicted that has never been reported before. This phase is dynamically stable and possesses lower free energy at elevated temperatures. Additionally, a few metastable candidates are also identified.

Advisor(s)

Chernatynskiy, Aleksandr V.

Committee Member(s)

Medvedeva, Julia E.
Vojta, Thomas
Hor, Yew San
Choudhury, Amitava

Department(s)

Physics

Degree Name

Ph. D. in Physics

Publisher

Missouri University of Science and Technology

Publication Date

Summer 2024

Pagination

x, 88 pages

Note about bibliography

Includes_bibliographical_references_(pages 77-87)

Rights

©2024 Qi Zhang , All Rights Reserved

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 12448

Download

Included in

Physics Commons

Share

 
COinS