Crystal structure determines properties of materials. With the crystal structure of a chemical substance, many physical and chemical properties can be predicted by first-principles calculations or machine learning models. Since it is relatively easy to generate a hypothetical chemically valid formula, crystal structure prediction becomes an important method for discovering new materials. In our previous work, we proposed a contact map-based crystal structure prediction method, which uses global optimization algorithms such as genetic algorithms to maximize the match between the contact map of the predicted structure and the contact map of the real crystal structure to search for the coordinates at the Wyckoff Positions(WP). However, when predicting the crystal structure with high symmetry, we found that the global optimization algorithm has difficulty to find an effective combination of WPs that satisfies the chemical formula, which is mainly caused by the inconsistency between the dimensionality of the contact map of the predicted crystal structure and the dimensionality of the contact map of the target crystal structure. This makes it challenging to predict the crystal structures of high-symmetry crystals. In order to solve this problem, here we propose to use PyXtal to generate and filter random crystal structures with given symmetry constraints based on the information such as chemical formulas and space groups. With contact map as the optimization goal, we use differential evolution algorithms to search for non-special coordinates at the Wyckoff positions to realize the structure prediction of high-symmetry crystal materials. Our experimental results show that our proposed algorithm CMCrystalHS can effectively solve the problem of inconsistent contact map dimensions and predict the crystal structures with high symmetry.
Objective crystallographic symmetry classifications of a noisy crystal pattern with strong Fedorov type pseudosymmetries and its optimal image-quality enhancement
SymmCD: Symmetry-Preserving Crystal Generation with Diffusion Models
McGill University（麦吉尔大学）；Mila；École Polytechnique Fédérale de Lausanne（洛桑联邦理工学院）；University of North Carolina at Charlotte（北卡罗来纳大学夏洛特分校）；Intel Labs（英特尔实验室）
Breaking crystalline symmetry of epitaxial SnTe films by strain
SnTe属于最近发现的拓扑晶体绝缘体类别。在这里，我们研究了线缺陷的形成，打破晶体对称性的应变在薄SnTe膜。采用分子束外延技术在晶格和热膨胀系数失配的CdTe衬底上生长了应变SnTe（111）薄膜。为了分析SnTe薄膜的结构特性，我们应用{ \em in situ}反射高能电子衍射，X射线反射计，高分辨率X射线衍射，倒易空间映射，和扫描隧道显微镜。这种全面的分析方法揭示了孪晶结构，拉伸应变，双层表面台阶和位错线缺陷形成高度有序的位错网络的厚膜与局部应变高达31\%，打破平移晶体对称性。
Information-theoretic point symmetry classifications/quantifications of an electron diffraction spot pattern from a crystal with strong translational pseudosymmetry
Symmetry Conditions for Non-reciprocal Light Propagation in Magnetic Crystals
最近的研究表明，在低对称磁性晶体中，光学过程中存在着互易性的破坏。在这些晶体中，对于反向传播的光束，光速可以不同。相应地，它们可以显示出强的方向各向异性，例如方向相关吸收，也称为方向二向色性[S. Bordács等人，8，734（2012）; M. Saito等人，日本物理学会77，013705（2008）]。基于对称性的考虑，我们确定的磁点组的材料，可以主机这样的方向各向异性，也提供了一个列表的可能的候选材料来观察这些现象。在大多数情况下，晶体的对称性不仅允许光学过程的方向各向异性，而且还允许粒子束和标量波的传播。我们还预测了新类型的定向光学各向异性-除了光磁电效应和磁手征二向色性迄今调查-并指定磁点群的晶体，它们可以出现。
Nature self-imposed limits and existence of intrinsically incomparable crystal (ligand) field parameter sets for transition ions at orthorhombic, monoclinic, and triclinic symmetry sites in crystals: pitfalls and blessings
WyckoffDiff -- A Generative Diffusion Model for Crystal Symmetry
Department of Computer and Information Science (IDA), Linköping University, Sweden（计算机与信息科学系（IDA），_linköping大学，瑞典）；Department of Physics, Chemistry and Biology (IFM), Linköping University, Sweden（物理、化学与生物学系（IFM），_linköping大学，瑞典）
Representations of the symmetry groups of infinite crystals
Université de Rennes（雷恩大学）；CNRS, Institut de recherche mathématique de Rennes, IRMAR（法国国家科学研究中心，雷恩数学研究所，IRMAR）；Sorbonne Université（索邦大学）；CNRS, Muséum National d’Histoire Naturelle, Institut de minéralogie, de physique des matériaux et de cosmochimie, IMPMC（法国国家科学研究中心，国家自然历史博物馆，矿物学、材料物理与宇宙化学研究所，IMPMC）
Electron-Nuclear Interactions as a Test of Crystal-Field Parameters for Low Symmetry Systems: Zeeman-Hyperfine Spectroscopy of Ho$^{3+}$ Doped Y$_2$SiO$_5$
Reproduction of the electronic and magnetic structure of the low symmetry sites of Y$_{2}$SiO$_{5}$ doped with Sm$^{3+}$ via a parameterized crystal-field model
参数化晶场分析的六倍和七倍协调，C $_{1}$对称Sm $^{3+}$中心在Y $_{2}$ SiO $_{5}$，广泛的光谱数据的基础上跨越红外光学区域。除了先前确定的$^{6}$ H $_{5/2}$ Z $_{1}$和$^{4}$ G $_{5/2}$ A $_{1}$状态的$g$张量之外，还利用了沿着多个晶体学方向进行的激光位点选择性激发和荧光光谱以及塞曼吸收光谱。由此产生的分析给出了很好的近似的实验能级和磁分裂，产生晶体场参数与其他几个镧系元素离子，这种分析是可用的。
