title: Crystal structure prediction and hydrogen-bond symmetrization of solid hydrazine under high pressure: a first-principles study.
abstract: In this article, the crystal structure of solid hydrazine under pressure has been extensively investigated using ab initio evolutionary simulation methods. Calculations indicate that hydrazine remains both insulating and stable up to at least 300 GPa at low temperatures. A structure with P2₁ symmetry is found for the first time through theoretical prediction in the pressure range 0-99 GPa and it is consistent with previous experimental results. Two novel structures are also proposed, in the space groups Cc and C2/c, postulated to be stable in the range 99-235 GPa and above 235 GPa, respectively. Below 3.5 GPa, C2 symmetry is found originally, but it becomes unstable after adding the van der Waals interactions. The P2₁→Cc transition is first order, with a volume discontinuity of 2.4%, while the Cc→C2/c transition is second order with a continuous volume change. Pressure-induced hydrogen-bond symmetrization occurs at 235 GPa during the Cc→C2/c transition. The underlying mechanism of hydrogen-bond symmetrization has also been investigated by analysis of electron localization functions and vibrational Raman/IR spectra.
authors: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012 People's Republic of China.
authors: Hua-Di
authors: HD
authors: Zhang
authors: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012 People's Republic of China.
authors: Song-Kuan
authors: SK
authors: Zheng
authors: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012 People's Republic of China.
authors: Xi-Lian
authors: XL
authors: Jin
authors: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012 People's Republic of China.
authors: Shu-Qing
authors: SQ
authors: Jiang
authors: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012 People's Republic of China.
authors: Zhi
authors: Z
authors: He
authors: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012 People's Republic of China.
authors: Bing-Bing
authors: BB
authors: Liu
authors: State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012 People's Republic of China.
authors: Tian
authors: T
authors: Cui
keywords: USPEX; computational materials discovery; crystal structure prediction; high-pressure modelling; hydrazine; hydrogen bonding