• DOI:10.1063/5.0077343
• Corpus ID: 246295031

Evidence for multiple liquid–liquid phase transitions in carbon, and the Friedel ordering of its liquid state

@article{Dharmawardana2022EvidenceFM,
  title={Evidence for multiple liquid–liquid phase transitions in carbon, and the Friedel ordering of its liquid state},
  author={M. W. Chandre Dharma-wardana and Dennis D. Klug},
  journal={Physics of Plasmas},
  year={2022}
}

• M. Dharma-wardana, D. Klug
• Published 5 July 2021
• Physics, Chemistry
• Physics of Plasmas

Carbon, the fourth most abundant element in the Universe forms a metallic fluid with transient covalent bonds on melting. Its liquid-liquid phase transitions, intensely sought using simulations had been elusive. Here we use density functional theory (DFT) simulations with up to 108 atoms using molecular dynamics, as well as one-atom DFT as implemented in the neutral pseudo-atom method where multi-atom effects are treated by ion-ion correlation functionals. Both methods use electron-electron exchange correlation functionals for electron many-body effects. Here we show using both methods, that liquid carbon displays multiple liquid-liquid transitions linked to changes in coordination number in the density range 3 g/cm, to ∼ 6 g/cm when a coordination number of 12 is reached. The transitions disappear by 4 eV in temperature. The calculated pressures and transition densities are shown to be sensitive to the exchange-correlation functionals used. Significantly, we find that a simple metallic model yields the structure factors and thermodynamics with quantitative accuracy, without invoking any covalent-bonding features. The ion-ion structure factor for these densities and temperatures is found to have a subpeak tied to twice the Fermi wavevector, constraining the fluid in momentum space. The dominant Friedel oscillations forming the pair interactions correlate the ions and drive the multiple liquid-liquid phase transitions. Our results suggest that liquid carbon typifies a class of fluids whose structure is ordered by the long-ranged Friedel oscillations in the pair-potentials. These results are critical to terrestrial and astrophysical studies, inertial fusion using carbon drivers, refined shock experiments, and in seeking new carbon-based materials. PACS numbers: 52.25.Jm,52.70.La,71.15.Mb,52.27.Gr ∗ Email address: [e-mail]