Algorithms for real-time time-dependent density functional theory and calculation of phase diagrams for two-dimensional phase-change materials
- Daniel A. Rehn.
- [Stanford, California] : [Stanford University], 2018.
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- Physical description
- 1 online resource.
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|3781 2018 R||In process|
- Rehn, Daniel Adam, author.
- Cai, Wei, 1977- degree supervisor.
- Reed, Evan J., degree supervisor.
- Lindenberg, Aaron Michael, degree committee member.
- Pop, Eric, 1975- degree committee member.
- Salleo, Alberto, degree committee member.
- Stanford University. Department of Mechanical Engineering.
- ["Two-dimensional materials have found use in a wide range of engineering applications, owing in part to their unique properties not found in the bulk and their potential to enable fabrication of devices that approach atomic sizes. The inherently quantum mechanical nature of 2D materials can be treated using density functional theory (DFT)-based methods, with some limitations that can in principle be addressed with the time-dependent formulation of DFT, known as time-dependent density functional theory (TDDFT). Here, we explore the use of DFT and TDDFT for applications of 2D materials, with two primary focuses: (1) the implementation and analysis of numerical integration schemes for time-domain TDDFT and associated applications to 2D and bulk materials properties and (2) the application of ground-state DFT to the study of thermodynamic properties of 2D materials that undergo structural phase transformations under electrostatic gating. Towards focus 1, we have implemented a variety of implicit and explicit integration schemes in the context of plane-wave real-time TDDFT and assessed the accuracy, stability, and computational cost of these methods. We find that for plane-waves, high-order explicit multi-step methods, including Adams-Bashforth and Adams-Bashforth-Moulton methods, outperform commonly-used methods including Crank-Nicolson and Runge-Kutta. We have developed a code, called rt-tddft, as an extension to the popular Quantum ESPRESSO code, which will enable researchers performing ground-state plane-wave DFT calculations to immediately benefit from our time-domain integration schemes. The code is written in object-oriented Fortran and is designed using object-oriented design patterns and built-in testing. We also apply the code to a new time-domain formulation of the adiabatic connection fluctuation-dissipation theorem (ACFDT) to compute electron correlation energies, an application especially relevant to van der Waals interactions in 2D materials systems. Towards focus 2, we have developed modeling methods to predict the phase transformation properties and phase diagrams of electrostatically-gated 2D materials. Using DFT-based calculations, we are able to predict the critical charge and critical voltage required to induce a structural phase transformation in a variety of 2D materials, and also determine how these critical values change with temperature. Using these methods, we are able to map out detailed phase diagrams for different 2D materials systems. In addition, we study the potential to use the electrostatic gating mechanism to absorb heat from the surroundings, an effect we term the electrostaticaloric effect. The methods we develop are useful for a variety of realistic engineering applications, including the use of 2D materials for applications in phase-change memory, controllable atomic-scale heat absorbers, and atomic sensors."]
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- Submitted to the Department of Mechanical Engineering.
- Thesis Ph.D. Stanford University 2018.
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