二氧化硅和铝磷酸盐中α到β相变的结构手性和自然光学活性
Structural Chirality and Natural Optical Activity across the $α$-to-$β$ Phase Transition in SiO$_2$ and AlPO$_4$ from first-principles
AI总结：
本研究通过从头原理计算揭示了二氧化硅和铝磷酸盐在α到β相变过程中，光学旋转符号由原子尺度手性决定，而非空间群符号中的螺轴手性。
摘要：
自然光学活性（NOA），即材料使偏振光平面旋转的能力，传统上被认为与结构手性相关。然而，这种关系往往被过度简化，导致概念误解，尤其是在试图直接关联结构手性与光学旋转力时。实际上，手性与NOA的关系更为复杂：光学活性可以在手性和非手性晶体结构中出现，且旋转的符号不能简单地从空间群的手性推断出来。在本工作中，我们通过从头原理研究了二氧化硅和铝磷酸盐晶体中的自然光学活性，重点研究其从高对称六方（P6_422或P6_222）到低对称三斜（P3_121或P3_221）空间群的对称性相变。这种相变由区心Γ_3声子模的凝聚驱动，改变了空间群符号中给出的螺轴类型，但保持了光学活性的符号不变。通过跟踪相变路径中结构和光学响应的变化，我们澄清了这种行为的微观起源。我们证明，光学旋转的符号不是由空间群符号中给出的螺轴名义手性决定的，而是由结构中最极化原子的原子尺度手性决定的。
英文摘要：
Natural optical activity (NOA), the ability of a material to rotate the plane of polarized light, has traditionally been associated with structural chirality. However, this relationship has often been oversimplified, leading to conceptual misunderstandings, particularly when attempts are made to directly correlate structural handedness with optical rotatory power. In reality, the relationship between chirality and NOA is more nuanced: optical activity can arise in both chiral and achiral crystal structures, and the sign of the rotation cannot necessarily be inferred from the handedness of the space group. % In this work, we conduct a first-principles investigation of natural optical activity in SiO$_2$ and AlPO$_4$ crystals, focusing on their enantiomorphic structural phase transition from high-symmetry hexagonal ($P6_422$ or $P6_222$) to low-symmetry trigonal ($P3_121$ or $P3_221$) space groups. This transition, driven by the condensation of a zone-center $Γ_3$ phonon mode, reverses the screw axis type given by the space group symbol while leaving the sign of the optical activity unchanged. By following the evolution of the structure and the optical response along the transition pathway, we clarify the microscopic origin of this behavior. We demonstrate that the sense of optical rotation is determined not by the nominal helicity of the screw axis given in the space group symbol, but by the atomic-scale helicity of the most polarizable atoms of the structure.
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