Evolution of amorphous carbon across densities: An inferential study

Abstract

In this paper, we offer large and realistic models of amorphous carbon spanning densities from 0.95 g/cm3 to 3.5 g/cm3. The models are designed to agree as closely as possible with experimental diffraction data while simultaneously attaining a local energy minimum of a density functional Hamiltonian. The structure varies dramatically from interconnected wrapped and defective sp2 sheets at 0.95 g/cm3 to a nearly perfect tetrahedral topology at 3.5 g/cm3. Force Enhanced Atomic Refinement (FEAR) was used and is shown here to be advantageous relative to conventional ab initio melt quench methods. We thoroughly characterize our models by computing structural, electronic and vibrational properties. The vibrational density of states of the 0.95 g/cm3 model is strikingly similar to monolayer amorphous graphene. Our sp2/sp3 ratios are close to experimental predictions where available.