中国物理B ›› 2021, Vol. 30 ›› Issue (5): 57102-057102.doi: 10.1088/1674-1056/abdb1b

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

Zi Li(李孜)1, Wei-Jie Li(李伟节)1, Cong Wang(王聪)1,†, Dafang Li(李大芳)1, Wei Kang(康炜)2, Xian-Tu He(贺贤土)1,2, and Ping Zhang(张平)1,2,‡   

  1. 1 Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;
    2 Center for Applied Physics and Technology, Peking University, Beijing 100871, China
  • 收稿日期:2020-11-24 修回日期:2021-01-05 接受日期:2021-01-13 出版日期:2021-05-14 发布日期:2021-05-14
  • 通讯作者: Cong Wang, Ping Zhang E-mail:wang_cong@iapcm.ac.cn;zhang_ping@iapcm.ac.cn
  • 基金资助:
    Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0403200), the National Natural Science Foundation of China (Grant Nos. 11775031, 11975058, 11625415, and 11675024), and the Science Challenge Project (Grant No. TZ2016001).

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

Zi Li(李孜)1, Wei-Jie Li(李伟节)1, Cong Wang(王聪)1,†, Dafang Li(李大芳)1, Wei Kang(康炜)2, Xian-Tu He(贺贤土)1,2, and Ping Zhang(张平)1,2,‡   

  1. 1 Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;
    2 Center for Applied Physics and Technology, Peking University, Beijing 100871, China
  • Received:2020-11-24 Revised:2021-01-05 Accepted:2021-01-13 Online:2021-05-14 Published:2021-05-14
  • Contact: Cong Wang, Ping Zhang E-mail:wang_cong@iapcm.ac.cn;zhang_ping@iapcm.ac.cn
  • Supported by:
    Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0403200), the National Natural Science Foundation of China (Grant Nos. 11775031, 11975058, 11625415, and 11675024), and the Science Challenge Project (Grant No. TZ2016001).

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 Hugoniot 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.

关键词: first-principles, warm dense, x-ray absorption spectrum, ammonia

Abstract: 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 Hugoniot 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.

Key words: first-principles, warm dense, x-ray absorption spectrum, ammonia

中图分类号:  (Density functional theory, local density approximation, gradient and other corrections)

  • 71.15.Mb
78.70.Dm (X-ray absorption spectra) 61.05.cj (X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.)