Formation and properties of astrophysical carbonaceous dust

TL;DR

This paper uses atomistic modeling and density functional theory to analyze carbon cluster formation, revealing new insights into nucleation sizes and temperature effects in astrophysical dust formation.

Contribution

It introduces an atomistic approach to dust nucleation, calculating critical sizes and nucleation rates based on carbon cluster geometries and energies, improving upon classical theories.

Findings

Critical cluster sizes are linked to geometric transitions in carbon clusters.

Nucleation is enhanced at low temperatures and suppressed at high temperatures.

Clusters with sizes 8 and 27 are key in the nucleation process.

Abstract

The classical theory of grain nucleation suffers from both theoretical and predictive deficiencies. We strive to alleviate these deficiencies in our understanding of dust formation and growth by utilizing an atomistic model of nucleation. Carbon cluster geometries are determined with a set of global minimization algorithms. Using density functional theory, the binding energies of carbon clusters from $n=2$ to $n=99$ are then calculated. These energies are used to calculate the critical size and nucleation rate of carbon clusters. We find that the critical cluster size is largely determined by the changes in geometry of the clusters. Clusters with size $n=27$ and $n=8$, roughly corresponding to the transition from ring-to-fullerene geometry and chain-to-ring geometry respectively, are the critical sizes across the range of temperature and saturation where nucleation is significant. In contrast to the classical theory, nucleation is enhanced at low-temperatures, and suppressed at high temperatures. These results will be applied to a modified chemical evolution code using results from supernova simulations.