Belosludov Rodion V, Gets Kirill V, Zhdanov Ravil K, Bozhko Yulia Y, Belosludov Vladimir R
Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan.
Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, 630090, Russia.
Sci Rep. 2025 Apr 30;15(1):15190. doi: 10.1038/s41598-025-97595-y.
In this work, the nature of the boson peak associated with the interaction between acoustic and optical phonons is revealed in low-density amorphous LDA ice and hexagonal crystalline ice (I) using the lattice dynamics method within the SPC/E water model. The appearance of these vibrations is associated with proton disordering in ice I and with both protons and oxygen atoms in LDA ice. Based on calculation of the eigenfrequencies and eigenvectors of vibrations, dispersion curves were constructed, the dynamics of water molecules involved in various vibrations was characterized, and the spatial molecular distribution was visualized. This enabled the identification of the structural inhomogeneities of the molecules participating in the vibrations. The presence of a boson peak in both amorphous LDA ice and crystalline ice I and its relation to proton or molecular disorder are shown. The collective nature of the vibrations that form the boson peak is discussed. The distances between neighboring water molecules involved in high-amplitude boson peak vibrations in both LDA and I ices are below the average value and are located more closely to each other. Analysis of the obtained data showed that the appearance of the boson peak can be associated with the interaction of acoustic vibrations with the vibrations of structural inhomogeneities, which form low-energy optical vibrations. This paper shows for the first time a boson peak-like anomaly in the heat capacity of the structure of crystalline ice I, as well as amorphous LDA ice. Our work confirms that the mechanism of formation of the boson peak is associated with acousto-optical resonance, leading to pseudo van Hove singularities of the acoustic phonon branches, and is also associated with the densification of low-frequency optical branches, which are quasi-degenerate with longitudinal acoustic vibrations, and leads to the appearance of excess low-frequency vibrations.
在这项工作中，利用SPC/E水模型中的晶格动力学方法，揭示了低密度非晶态LDA冰和六方晶态冰（I）中与声学声子和光学声子相互作用相关的玻色子峰的本质。这些振动的出现与冰I中的质子无序以及LDA冰中的质子和氧原子均有关。基于振动本征频率和本征向量的计算，构建了色散曲线，表征了参与各种振动的水分子的动力学，并可视化了空间分子分布。这使得能够识别参与振动的分子的结构不均匀性。展示了非晶态LDA冰和晶态冰I中玻色子峰的存在及其与质子或分子无序的关系。讨论了形成玻色子峰的振动的集体性质。LDA冰和I冰中参与高振幅玻色子峰振动的相邻水分子之间的距离低于平均值，且彼此靠得更近。对所得数据的分析表明，玻色子峰的出现可能与声学振动与结构不均匀性的振动相互作用有关，这些结构不均匀性形成了低能光学振动。本文首次展示了晶态冰I以及非晶态LDA冰结构的热容中类似玻色子峰的异常。我们的工作证实，玻色子峰的形成机制与声光共振有关，导致声学声子分支出现伪范霍夫奇点，并且还与低频光学分支的致密化有关，这些低频光学分支与纵向声学振动准简并，从而导致出现额外的低频振动。
