A combined study of vibrational and thermodynamic properties of metaboric acid (BOH)₃O₃ crystal polymorphs α, β, and γ were obtained through density functional theory (DFT) calculations in an attempt to resolve the conflicting assignments that currently exist in the literature for them. A complete correlation between the normal-mode assignment and vibrational signatures to distinguish particular features of each metaboric acid polymorph, in particular, those related to motions of the planar layers in α-(BOH)₃O₃, with a level of detail surpassing essays based on previous published experimental works has been achieved. Besides, no DFT-based research work was published early on the (BOH)₃O₃ polymorph vibrational properties, and our DFT-simulated infrared and Raman spectra for all metaboric acid polymorphs agree very well with experiment. Comparison of the previously published experimental IR and Raman spectroscopic results with predictions from higher levels DFT calculations allows identification of the in-plane and out-of-plane B–O bending modes. For example, the strongest measured (DFT-calculated) Raman modes of α-(BOH)₃O₃ at 591 and 797 cm^–1 (599 and 810 cm^–1) are identified as vibrational signatures of breathing B₃O₃/A_g in-plane modes, while the shoulder in the lattice modes region at 135 (143) cm^–1 is the vibrational signature of the bending B₃O₃/B_1g out-of-plane mode. Phonon-dispersion bands and their respective phonon densities of states were also evaluated for each system, as well as temperature-dependent curves for entropy, enthalpy, free energy, heat capacity, and Debye temperature. Phonon dispersion curves are singular for each (BOH)₃O₃ species, and a consistent gap decrease between the lowest and highest frequency vibrational bands was observed. The DFT-based calculations also revealed that the noncovalent interactions prevalent in the α and β crystals lead to significant differences with respect to the thermodynamic properties in comparison with the γ phase.

中文翻译：

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在密度泛函理论框架内偏硼酸多晶型物α-，β-和γ-（BOH）₃ O _3的振动模式以及声子和热力学性质

通过密度泛函理论（DFT）计算获得了偏硼酸（BOH）₃ O ₃晶体多晶型物α，β和γ的振动和热力学性质的组合研究，以试图解决文献中目前存在的相互冲突的分配问题。他们。在正常模式分配和振动特征之间有完整的关联，以区分每个偏硼酸多晶型物的特定特征，尤其是那些与α-（BOH）₃ O ₃中的平面层的运动有关的特征，其详细程度超过了论文基于以前发表的实验作品已经实现。此外，关于（BOH）₃ O _3的早期基于DFT的研究工作尚未发表。多晶型物的振动特性，我们的DFT模拟的所有偏硼酸多晶型物的红外光谱和拉曼光谱与实验非常吻合。通过将先前发布的实验IR和拉曼光谱结果与更高水平DFT计算的预测结果进行比较，可以识别平面内和平面外B–O弯曲模式。例如，在591和797 cm ^–1（599和810 cm ^–1）处测量到的最强的α-（BOH）₃ O ₃拉曼模式被识别为呼吸B ₃ O ₃ / A的振动信号。_g平面模式，而肩部处于格子模式区域时为135（143）cm ^–1是弯曲B ₃ O ₃ / B _1g平面外模式的振动信号。还评估了每个系统的声子弥散带及其各自的声子密度，以及熵，焓，自由能，热容和德拜温度的温度相关曲线。每种（BOH）₃ O _3的声子弥散曲线都是奇异的，并且在最低和最高频率的振动带之间观察到一致的间隙减小。基于DFT的计算还表明，与γ相相比，α和β晶体中普遍存在的非共价相互作用导致热力学性质的显着差异。