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Atomistic coarse-grained hybrid modeling of ferroelectric materials
The performances of ferroelectric materials used in electro-mechanical/optical devices are strongly affected by the material surfaces, domain walls and grain boundaries. A good understanding of the formations and behaviors of these heterogeneities in relation to their vast homogeneous surroundings is crucial to the device design optimizations. An atomistic coarse-grained hybrid modeling technique has been developed for simulations of ferroelectric materials with isolated heterogeneities. It merges a fully atomistic (FA) description for the heterogeneities with an efficient coarse-grained (CG) modeling for the vast homogeneous regions away from the heterogeneities. Aimed at quasistatic behaviors, the model employs a statistical mechanics approach, in which the positions of the atomic species in the FA regions and the CG nodes at the FA-CG interfaces are sampled by the Monte Carlo simulations to calculate the system properties as ensemble averages. It avoids the time limitation of atomic motion integration and enables a rigorous implementation of the massless shell model for interatomic potentials. The coarse graining uses a quasicontinuum treatment that combines continuum deformation analysis with atomistic energy calculation using the same interatomic potentials for consistency. It also includes lattice vibration energy estimated with the local harmonic approximation for finite temperature simulations, and multiple species-specific meshes for modeling the atomic/subatomic phase evolutions with temperature and loading. ^ The model and its component performances have been evaluated for PbTiO 3. A shell model in good agreement with the experimental data on PbTiO 3 has been obtained from the FA simulation results. The CG simulations of homogeneous PbTiO3 have been examined against the corresponding FA results. The CG method is found to be sufficiently accurate for linear piezoelectric response and below 700K. Finally, the hybrid method has been applied successfully to study the surface, bicrystal gain boundaries and domain walls of PbTiO3. The thicknesses calculated for the three types of 90° domain walls are in good agreement with the experimental measurements. The method has also been applied to simulate surface indentation of silicon successfully, demonstrating its applicability for other materials with atomic heterogeneities of interest.^
Zeng, Yun, "Atomistic coarse-grained hybrid modeling of ferroelectric materials" (2016). ETD collection for University of Nebraska - Lincoln. AAI10104393.