Evolution of amorphous carbon across densities: an inferential study

TL;DR

This study develops realistic models of amorphous carbon across a wide density range, using FEAR, and compares structural, electronic, and vibrational properties with experimental data.

Contribution

It introduces a novel modeling approach for amorphous carbon across densities, demonstrating FEAR's advantages over traditional methods.

Findings

Models match experimental diffraction data closely.

Vibrational spectra resemble amorphous graphene at low density.

Structural ratios align with experimental predictions.

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 minimum of a density functional Hamilto- nian. 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 Refine- ment (FEAR) was used and is shown here to be computationally superior and more experimentally realistic than conventional ab initio melt quench methods. We thoroughly characterize our models by computing structural, electronic and vibrational spectra. 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, a consequence of compelling a satisfactory fit for pair correlation function.