Ab initiocalculation of properties of carbon in the amorphous and liquid states

We have carried out a detailed investigation of liquid carbon (l-C) at T≃5000 K, and quenched amorphous carbon (a-C) at room temperature, using a first-principles molecular-dynamics method. In this paper we report calculations performed for a fixed density corresponding to low pressures. From our results, which agree well with the limited experimental information available, we analyze the short-range order, particularly the fractions of sp, ${\mathit{sp}}^2$, and ${\mathit{sp}}^3$ sites, and the electronic properties of the two systems. In addition, we discuss new features of a-C and l-C, predicted by our calculation, and present an analysis of some models proposed in the literature to account for their electronic and bonding properties, as well as of recent controversial experiments.