基于非简谐晶格模型的准简谐自由能完全优化：在纤锌矿GaN和ZnO的热膨胀与热释电中的应用
Full optimization of quasiharmonic free energy with anharmonic lattice model: Application to thermal expansion and pyroelectricity of wurtzite GaN and ZnO
AI总结：
本研究提出基于IFC重整化的准简谐近似有限温度结构优化理论，同时优化胞形与原子坐标，准确复现纤锌矿GaN和ZnO的热膨胀及热释电行为，并提出可兼顾效率与精度的约束优化通用方案。
摘要：
我们提出了一种在准简谐近似（QHA）框架下实现有限温度结构优化的理论与计算方案。该理论基于一种随晶体结构变化更新原子间力常数的高效方案，我们将其称为IFC重整化。胞形形状与原子坐标被同等对待并同时优化。我们将该理论应用于纤锌矿GaN和ZnO的热膨胀与热释电现象，准确复现了实验观测到的行为。此外，我们提出了一种通用方案，可在减少有效自由度数量的约束优化中获得最低阶的正确温度（T）依赖关系，这有助于在几乎不牺牲精度的前提下开展高效的QHA计算。通过与全自由度优化结果对比，我们证明该方案在GaN和ZnO体系中运行良好。
英文摘要：
We present a theory and a calculation scheme of structural optimization at finite temperatures within the quasiharmonic approximation (QHA). The theory is based on an efficient scheme of updating the interatomic force constants with the change of crystal structures, which we call the IFC renormalization. The cell shape and the atomic coordinates are treated equally and simultaneously optimized. We apply the theory to the thermal expansion and the pyroelectricity of wurtzite GaN and ZnO, which accurately reproduces the experimentally observed behaviors. Furthermore, we point out a general scheme to obtain correct $T$ dependence at the lowest order in constrained optimizations that reduce the number of effective degrees of freedom, which is helpful to perform efficient QHA calculations with little sacrificing accuracy. We show that the scheme works properly for GaN and ZnO by comparing with the optimization of all the degrees of freedom.
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