Pressure-induced structural change of liquid carbon studied by ab initio molecular-dynamics simulations

We have Studied the structural and the electronic properties of liquid carbon as a function of the pressure using ab initio molecular-dynamics simulation. We are particularly concerned with the pressure-induced structural change. When the density (pressure) is increased from 2.9 g/cm(3) (16 GPa) to 11.6 g/cm(3) (2000 GPa) at the constant temperature of 9000 K, the structure of liquid carbon changes drastically as follows: The peaks of the radial distribution functions g(r) shift to shorter distances and become higher and sharper, and the average coordination number increases from three to eight. The structure factor S(k) changes its shape qualitatively at extremely high pressure and becomes similar to those of liquid Si and Ge at ambient pressure, which is characterized by a shoulder on the high-wavenumber side of the first peak of S(k). We have shown that, with increasing density, the bonding character changes from covalent bonding to metallic bonding based on the bond-angle distribution, the electron density distribution and the overlap population. We have also investigated the dynamical properties of liquid carbon such as the velocity autocorrelation function and the self-diffusion coefficient in relation to the pressure-induced structural change.