The mixing of organic cations represents yet another direction to explore in the field of chiral organic-inorganic hybrid metal halides (OIHMH). Here, we perform structural optimizations, electronic structures, and nonlinear optical (NLO) studies using density functional theory of two recently synthesized chiral OIHMHs, [R-MePEA][C3A]PbBr₄ and [R-MePEA][C4A]PbBr₄, with mixed chiral arylammonium and achiral alkylammonium cations. We find that the noncovalent weak interactions (e.g., Br···NH interactions) play an important role in the description of these OIHMHs. Our study further indicates that the two noncentrosymmetric compounds exhibit relatively wide bandgaps (∼3.5 eV), strong second harmonic generation (SHG) responses (∼0.5–1.5 × KDP), and moderate birefringence (∼0.088 at 1064 nm), indicating possible applications for NLO materials. Atom response theory analysis reveals that the SHG responses are determined mainly by the occupied Br 3p nonbonding orbitals as well as by the unoccupied Pb 5p orbitals, which shows the important contribution of the inorganic PbBr₄ layer to the nonlinear optical properties.

中文翻译：

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手性二维有机-无机杂化金属卤化物中的混合有机阳离子─非线性光学（NLO）性质的从头算研究


有机阳离子的混合代表了手性有机-无机杂化金属卤化物（OIHMH）领域的另一个探索方向。在这里，我们利用密度泛函理论对两种最近合成的手性 OIHMH [R-MePEA][C3A]PbBr ₄ 和 [R-MePEA] 进行结构优化、电子结构和非线性光学 (NLO) 研究。 [C4A]PbBr ₄ ，具有混合的手性芳基铵和非手性烷基铵阳离子。我们发现非共价弱相互作用（例如 Br·NH 相互作用）在这些 OIHMH 的描述中发挥着重要作用。我们的研究进一步表明，这两种非中心对称化合物表现出相对较宽的带隙（∼3.5 eV）、较强的二次谐波产生（SHG）响应（∼0.5–1.5 × KDP）和中等双折射（∼0.088 at 1064 nm），表明可能的应用对于 NLO 材料。原子响应理论分析表明，SHG响应主要由占据的Br 3p非键轨道以及未占据的Pb 5p轨道决定，这表明无机PbBr ₄ 层对非线性光学的重要贡献特性。