Description
- Abstract:
- The phase diagram of numerous materials of technological importance features high-symmetry high-temperature phases that exhibit phonon instabilities. Leading examples include shape-memory alloys, as well as numerous refractory and structural materials. The thermodynamics of these phases have proven challenging to handle via atomistic computational thermodynamic techniques, due to the occurrence of constant anharmonicity-driven hoping between local low-symmetry distortions, while maintaing a high-symmetry time-averaged structure. To compute the free energy in such phases, we propose to explore the system's potential energy surface by discrete sampling of local minima via a lattice gas Monte Carlo approach and by a continuous sampling via a lattice dynamics approach in the vicinity of each local minimum. Given the proximity of the local minima, it is necessary to carefully partition phase space using a Voronoi tessellation to constrain the domain of integration of the partition function, in order to avoid double-counting artifacts and enable an accurate harmonic treatment near each local minima. We consider two different examples to illustrate our method. As a prototypical example, bcc phase of Titanium at high temperature is explored. The advantage of the introduced method over previous scheme is the capability of this method to consider alloys. Therefore as another complicated example PtTi compound system is considered.
- Notes:
- Thesis (Ph.D. -- Brown University (2016)
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Citation
kadkhodaei, sara,
"Free Energy Calculation of Mechanically Unstable but Dynamically Stabilized Phases"
(2016).
Mechanics of Solids Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.7301/Z0CR5RRX
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Mechanics of Solids Theses and Dissertations
Theses and Dissertations for the Mechanics of Solids department....