Machine Learning simulations reveal oxygen's phase diagram and thermal properties at conditions relevant to white dwarfs.

Journal: Nature communications
Published Date: Jul 1, 2025

Abstract

Current studies show that oxygen does not aggregate into a polymeric phase even under pressures up to 10 TPa. To address the critical knowledge gap in understanding dense oxygen, here we show the complete polymerization process of oxygen, by using structure prediction methods. We determine the crystal structures of oxygen up to 1 PPa (1000 TPa), identifying a novel two-dimensionally bonded body-centered tetragonal (bct) phase and a fully polymerized hexagonal close-packed (hcp) phase. Electronic structure analysis reveals significant bond softening in the bct phase with increasing pressure, which may affect the dynamic behavior under finite temperatures. So, we employ the machine learning potential molecular dynamics and the two-phase method to construct the melting curve of oxygen up to 200 TPa (200 TPa, 23,740 K) and identify abnormal melting behavior beyond 100 TPa. We find oxygen exhibits higher thermal conductivity and lower isochoric heat capacity than helium at identical pressures. These results indicate that oxygen-rich envelopes may accelerate the cooling process of white dwarfs.

Authors

  • Yunlong Wang
    Department of Radiation Oncology, The Sixth Affiliated Hospital of Sun Yat-sen University, Guangzhou, China; Guangdong Institute of Gastroenterology, Guangdong Provincial Key Laboratory of Colorectal and Pelvic Floor Diseases, Guangzhou, China.
  • Jiuyang Shi
    National Laboratory of Solid State Microstructures, School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China.
  • Zhixin Liang
    School of Mechanical Engineering, Xi'an Jiaotong University, Xi'an 710049, China.
  • Tianheng Huang
    National Laboratory of Solid State Microstructures, School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China.
  • Junjie Wang
    School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China.
  • Chi Ding
    National Laboratory of Solid State Microstructures, School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China. chiding@nju.edu.cn.
  • Chris J Pickard
    Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
  • Hui-Tian Wang
    Center of Reproductive Medicine, The Third Hospital of Sun Yat-sen University, Guangzhou, Guangdong 510630, China.
  • Dingyu Xing
    National Laboratory of Solid State Microstructures, School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China.
  • Dongdong Ni
    Institute of Science and Technology for Deep Space Exploration, Nanjing University, Suzhou, China. ddni@nju.edu.cn.
  • Jian Sun
    Department Of Computer Science, University of Denver, 2155 E Wesley Ave, Denver, Colorado, 80210, United States of America.

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