用物理约束的生成模型加速缺陷敏感晶体结构精修,避免局部最优。
Physically-Constrained Autoencoder-Assisted Bayesian Optimization for Refinement of High-Dimensional Defect-Sensitive Single Crystalline Structure
- 用物理约束变分自编码器将高维衍射数据压缩到低维隐空间
- 结合贝叶斯优化在真实与隐空间同步最小化误差,提升精修效率
- 适用于复杂缺陷体系的高维结构优化,适合材料计算与实验协同研究
材料的物理性质和功能由全局晶体结构和局部缺陷共同决定。为建立结构-性能关系,不仅需要晶格对称性,还需定量描述缺陷。本文提出一种混合机器学习框架,将物理约束变分自编码器(pcVAE)与多种贝叶斯优化(BO)方法结合,系统加速并改进缺陷敏感晶体结构的精修。以反钙钛矿结构Ho2Ti2O7为模型体系,采用GSAS2软件进行里特维尔德精修基准测试。然而,此类材料体系的函数空间高度非线性,传统里特维尔德精修易陷入局部极小值,且无法充分探索整体函数空间,不利于大空间、高耗时的潜在区域发现。为此,本文采用预训练pcVAE辅助的贝叶斯优化与稀疏轴对齐贝叶斯优化,探索高维结构参数。pcVAE将包含数千个独立测量衍射峰的高维衍射数据投影至低维隐空间,同时保持尺度不变性和物理合理性。随后通过贝叶斯优化方法,在真实空间与隐空间分别最小化实验与模拟衍射图样的L2范数χ²误差,引导精修向潜在最优结构参数逼近。我们对比了不同pcVAE辅助的BO、非pcVAE辅助的BO以及传统里特维尔德精修的结果。
原文摘要 · Abstract (English)
Physical properties and functionalities of materials are dictated by global crystal structures as well as local defects. To establish a structure-property relationship, not only the crystallographic symmetry but also quantitative knowledge about defects are required. Here we present a hybrid Machine Learning framework that integrates a physically-constrained variational-autoencoder (pcVAE) with different Bayesian Optimization (BO) methods to systematically accelerate and improve crystal structure refinement with resolution of defects. We chose the pyrochlore structured Ho2Ti2O7 as a model system and employed the GSAS2 package for benchmarking crystallographic parameters from Rietveld refinement. However, the function space of these material systems is highly nonlinear, which limits optimizers like traditional Rietveld refinement, into trapping at local minima. Also, these naive methods don't provide an extensive learning about the overall function space, which is essential for large space, large time consuming explorations to identify various potential regions of interest. Thus, we present the approach of exploring the high Dimensional structure parameters of defect sensitive systems via pretrained pcVAE assisted BO and Sparse Axis Aligned BO. The pcVAE projects high-Dimensional diffraction data consisting of thousands of independently measured diffraction orders into a lowD latent space while enforcing scaling invariance and physical relevance. Then via BO methods, we aim to minimize the L2 norm based chisq errors in the real and latent spaces separately between experimental and simulated diffraction patterns, thereby steering the refinement towards potential optimum crystal structure parameters. We investigated and compared the results among different pcVAE assisted BO, non pcVAE assisted BO, and Rietveld refinement.
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