Discovering Minimum Energy Pathways via Distortion Symmetry Groups
Open Access
- Author:
- Munro, Jason
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 22, 2019
- Committee Members:
- Ismaila Dabo, Dissertation Advisor/Co-Advisor
Ismaila Dabo, Committee Chair/Co-Chair
Venkatraman Gopalan, Committee Member
Long-Qing Chen, Committee Member
Gerald Knizia, Outside Member - Keywords:
- Symmetry
Minimum Energy Pathways
Nudged Elastic Band
Density Functional Theory
Ferroelectric Switching - Abstract:
- Physical systems evolve from one state to another along paths of least energy barrier. Without a priori knowledge of the energy landscape, multidimensional search methods aim to find such minimum energy pathways between the initial and final states of a kinetic process. However in many cases, the user has to repeatedly provide initial guess paths, thus ensuring that the reliability of the final result is heavily user-dependent. Recently, the idea of "distortion symmetry groups'" as a complete description of the symmetry of a path has been introduced. Through this, a new framework is enabled that provides a powerful means of classifying the infinite collection of possible pathways into a finite number of symmetry equivalent subsets, and then exploring each of these subsets systematically using rigorous group theoretical methods. More specifically, symmetry-adapted perturbations can be generated and used as a tool to systematically lower the initial path symmetry, enabling the exploration of other low-energy pathways that may exist. The group and representation theory details behind this process are presented and implemented in a standalone piece of software (DiSPy). The method, which we name the distortion symmetry method (DSM), is then applied and is shown to lead to the discovery of new, previously hidden pathways for the case studies of bulk ferroelectric switching and domain wall motion in proper and improper ferroelectrics, as well as in multiferroic switching. These provide novel physical insights into the nucleation of switching pathways at experimentally observed domain walls in Ca3Ti2O7 and LiNbO3, as well as how polarization switching can proceed without reversing magnetization in BiFeO3. Furthermore, it is demonstrated how symmetry-breaking from a highly symmetric pathway can be used to probe the non-Ising (Bloch and Neel) polarization components integral to transient states involved in switching in PbTiO3. The distortion symmetry method is applicable to a wide variety of physical phenomena ranging from structural, electronic and magnetic distortions, diffusion, and phase transitions in materials.