First-principles calculations of K-shell x-ray absorption spectra for warm dense ammonia

• 作者: Zi Li Wei-Jie Li Cong Wang Dafang Li Wei Kang Xian-Tu He Ping Zhang
• 来源期刊: 中国物理B（英文版）
• 年，卷（期）: 2021,（5）
• 所属期刊栏目: CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
• 页码范围: 648-655
• 页数: 8页
• 语种: 英文
• DOI: 10.1088/1674-1056/abdb1b

摘要

The x-ray absorption spectroscopy is a powerful tool for the detection of thermodynamic conditions and atomic structures on warm dense matter.Here,we perform first-principles molecular dynamics and x-ray absorption spectrum calculations for warm dense ammonia,which is one of the major constituents of Uranus and Neptune.The nitrogen K-shell x-ray absorption spectrum (XAS) is determined along the Hugohiot curve,and it is found that the XAS is a good indicator of the prevailing thermodynamic conditions.The atomic structures at these conditions are ascertained.Results indicate that the ammonia could dissociate to NHx (x =0,1,or 2) fragments and form nitrogen clusters,and the ratios of these products change with varying conditions.The contributions to the XAS from these products show quite different characteristics,inducing the significant change of XAS along the Hugoniot curve.Further model simulations imply that the distribution of the peak position of atomic XAS is the dominant factor affecting the total XAS.