Peng Jie, Zhang Sijie, Refson Keith, Dove Martin T
College of Physics, Sichuan University, Chengdu, Sichuan 610065, People's Republic of China.
ISIS Facility, Harwell Campus, Chilton, Didcot, OX11 0QX, United Kingdom.
J Phys Condens Matter. 2021 Dec 16;34(9). doi: 10.1088/1361-648X/ac3e1f.
We report calculations of the crystal structures and lattice dynamics of the tetragonal and orthorhombic phases of the molecular crystal hydrogen cyanide, HCN, using density functional theory methods. By treating negative pressure as a proxy for raising temperature we show that the ferroelastic phase transition involves softening of a transverse acoustic mode, and confirm that the phase transition is discontinuous. Analysis of the complete phonon spectrum shows that the acoustic modes are responsible both for the very large thermal expansion seen in HCN and also for the thermodynamic driving force for the phase transition.
我们报告了使用密度泛函理论方法对分子晶体氰化氢（HCN）的四方相和正交相的晶体结构和晶格动力学的计算结果。通过将负压作为升高温度的替代指标，我们表明铁弹性相变涉及横向声学模式的软化，并证实该相变是不连续的。对完整声子谱的分析表明，声学模式既导致了HCN中观察到的非常大的热膨胀，也是相变的热力学驱动力。
