The structure in warm dense carbon

TL;DR

This study investigates the atomic structure and bonding characteristics of warm dense carbon across a wide pressure range, revealing persistent covalent bonds and changes in coordination and packing efficiency with temperature and pressure.

Contribution

It provides new insights into the structural behavior and covalent bonding in warm dense carbon under extreme conditions, extending previous understanding of its phase and properties.

Findings

Coordination numbers increase with density.

Persistent covalent bonds are observed up to 1000 GPa.

Double-peak structure indicates covalent bonds at high temperatures.

Abstract

The structure of the fluid carbon phase in the pressure region of the graphite, diamond, and BC8 solid phase is investigated. We find increasing coordination numbers with an increase in density. From zero to $30$ GPa, the liquid shows a decrease of packing efficiency with increasing temperature. However, for higher pressures, the coordination number increases with increasing temperature. Up to $1.5$ eV and independent of the pressure up to $1000$ GPa, a double-peak structure in the ion structure factors exists, indicating persisting covalent bonds. Over the whole pressure range from zero to $1000$ GPa, the fluid structure and properties are strongly determined by such covalent bonds.