[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"doc-detail-127268-en":3,"doc-seo-127268-105":30,"detail-sidebar-cat-0-en-105":92},{"code":4,"msg":5,"data":6},0,"success",{"doc_id":7,"user_id":8,"nickname":9,"user_avatar":10,"doc_module":4,"category_id":11,"category_name":12,"doc_title":13,"doc_description":14,"doc_content":15,"file_id":16,"file_url":17,"file_type":18,"file_size":19,"view_count":20,"is_deleted":4,"is_public":20,"is_downloadable":20,"audit_status":20,"page_count":21,"language":22,"language_code":23,"site_id":24,"html_lang":23,"table_of_contents":25,"faqs":26,"seo_title":27,"seo_description":14,"update_tm":28,"read_time":29},127268,2336475104736,"Quinn","https://ap-avatar.wpscdn.com/avatar/22000c4c5e0e5b17e70?x-image-process=image/resize,m_fixed,w_180,h_180&k=1786591360781797222",8,"Research & Report","Machine Learning simulations reveal oxygen’s phase diagram and thermal properties at conditions relevant to white dwarfs","Machine learning simulations investigate dense oxygen under ultrahigh pressures relevant to white dwarfs, addressing gaps in how oxygen polymerizes at extreme conditions. The study uses structure prediction to determine oxygen crystal phases up to 1 PPa, identifying a novel two-dimensionally bonded bct phase and a fully polymerized hcp phase. Bond softening in bct is analyzed, and machine-learning potential molecular dynamics plus a two-phase method build the melting curve to 200 TPa, revealing abnormal melting beyond 100 TPa. Results show oxygen’s thermal transport differs from helium and may speed white dwarf cooling.","Article [https://doi.org/10.1038/s41467-025-61390-0](https://doi.org/10.1038/s41467-025-61390-0)  \nMachine Learning simulations reveal oxygen’s phase diagram and thermal properties at conditions relevant to white dwarfs  \nReceived: 24 January 2024  \n\n| Accepted: 20 June 2025 |\n| --- |\n|  |\n| Check for updates |\n\nYunlong Wang1,5, Jiuyang Shi1,5, Zhixin Liang1, Tianheng Huang1, Junjie Wang1, Chi Ding1 , Chris J. Pickard 2,3, Hui-Tian Wang 1, Dingyu Xing1, Dongdong Ni4  & Jian Sun 1   \nCurrent 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 twodimensionally 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.  \nOxygen is one of the most abundant elements in the universe, possessing fascinating properties. Under pressures exceeding 96 GPa1,2, molecular oxygen transitions into a metallic phase and transforms into the ζ phase at around 100 GPa3,4. Sun et al. thoroughly investigated oxygen at pressures up to 10 TPa5. They predicted a transition from the molecular phase to a tetragonal phase with polymerized helical chains at 1.9TPa, followed by a layered monoclinic phase known as the chainmolecular phase (space group Fmmm) at 9.3TPa. Moreover, they demonstrated that oxygen maintains a superconducting temperature of 0.6K to 2.1 K at TPa pressures. Building upon the work ofSun et al.,  \n[Cogollo-Olivo et al. re-examined the oxygen phase boundaries at](Cogollo-Olivo et al. re-examined the oxygen phase boundaries at) finite temperatures within the 1–10 TPa pressure range6. These studies comprehensively demonstrate oxygen’s properties and states below 10 TPa. However, even under such extreme pressures, the lone pair electrons in oxygen structures persist, and the polymerization process of oxygen remains incompletely elucidated.  \nWith increasing pressure, diatomic molecules such as oxygen, hydrogen, fluorine and nitrogen gradually aggregate from the molecular phase into the polymeric phase. Hydrogen may exhibit an alternately interlayered structure7–9, while nitrogen, due to its unique outer  \n1National Laboratory of Solid State Microstructures, School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China. 2Department of Materials Science & Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, UK. 3Advanced Institute for Materials Research, Tohoku University 2-1-1 Katahira, Aoba, Sendai, Japan. 4Institute of Science and Technology for Deep Space Exploration, Nanjing  \nUniversity, Suzhou, China. 5These authors contributed equally: Yunlong Wang, Jiuyang Shi. e-mail: [chiding@nju.edu.cn](chiding@nju.edu.cn); [ddni@nju.edu.cn](ddni@nju.edu.cn);  \n[jiansun@nju.edu.cn](jiansun@nju.edu.cn)  \nelectron configuration, possesses highly stable nitrogen-nitrogen triple bonds. Beyond 100 GPa, nitrogen transforms into the cubic-gauche phase10,11, and there are many metastable polymeric nitrogen structures realized. Only fluorine and oxygen are known to remain undissociated and form polymeric phases under TPa pressure5,12. Flu","cbCait0j0yJWW4Gr","https://ap.wps.com/l/cbCait0j0yJWW4Gr","pdf",1019118,1,7,"English","en",105,"# Key findings\n## Predicted crystal structures up to 1 PPa\n## Electronic structure and bond softening\n## Melting curve up to 200 TPa\n## Thermal properties compared with helium\n# Scientific motivation","[{\"question\":\"What new oxygen phases are identified in the study under ultrahigh pressure?\",\"answer\":\"The work predicts a novel two-dimensionally bonded body-centered tetragonal (bct) phase up to 1 PPa and a fully polymerized hexagonal close-packed (hcp) phase.\"},{\"question\":\"How is oxygen’s melting behavior determined and what anomaly is observed?\",\"answer\":\"Machine-learning potential molecular dynamics with a two-phase method constructs the melting curve up to 200 TPa, showing abnormal melting behavior beyond 100 TPa.\"},{\"question\":\"How do oxygen’s thermal properties compare with helium at the same pressures?\",\"answer\":\"Oxygen exhibits higher thermal conductivity and a lower isochoric heat capacity than helium when pressure conditions are matched.\"}]","Machine Learning simulations reveal oxygen’s phase diagram and thermal properties at conditions relevant to white dwarfs | 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new oxygen phases are identified in the study under ultrahigh pressure?","Question",{"text":76,"@type":77},"The work predicts a novel two-dimensionally bonded body-centered tetragonal (bct) phase up to 1 PPa and a fully polymerized hexagonal close-packed (hcp) phase.","Answer",{"name":79,"@type":74,"acceptedAnswer":80},"How is oxygen’s melting behavior determined and what anomaly is observed?",{"text":81,"@type":77},"Machine-learning potential molecular dynamics with a two-phase method constructs the melting curve up to 200 TPa, showing abnormal melting behavior beyond 100 TPa.",{"name":83,"@type":74,"acceptedAnswer":84},"How do oxygen’s thermal properties compare with helium at the same pressures?",{"text":85,"@type":77},"Oxygen exhibits higher thermal conductivity and a lower isochoric heat capacity than helium when pressure conditions are 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