Analysis of a carbon dimer bound to a vacancy in iron using density functional theory and a new tight binding model

TL;DR

This paper introduces a new tight binding model for carbon in iron that accurately predicts the structure and energetics of a carbon dimer bound to a vacancy, aligning with recent DFT findings and enhancing atomistic modeling of steels.

Contribution

A novel tight binding model for carbon in iron is developed, capable of reproducing DFT results and analyzing the carbon dimer at vacancies in different iron phases.

Findings

The TB model accurately predicts the carbon dimer structure at vacancies.

DFT and TB analyses reveal factors influencing the dimer's orientation.

The model works for both concentrated and dilute carbon in bcc and fcc iron.

Abstract

Recent density functional theory (DFT) calculations by Foerst et al. have predicted that vacancies in both low and high carbon steels have a carbon dimer bound to them. This is likely to change the thinking of metallurgists in the kinetics of the development of microstructures. While the notion of a C2 molecule bound to a vacancy in Fe will potentially assume a central importance in the atomistic modeling of steels, neither a recent tight binding (TB) model nor existing classical interatomic potentials can account for it. Here we present a new TB model for C in Fe, based on our earlier work for H in Fe, which correctly predicts the structure and energetics of the carbon dimer at a vacancy in Fe. Moreover the model is capable of dealing with both concentrated and dilute limits of carbon in both bcc-Fe and fcc-Fe as comparisons with DFT show. We use both DFT and TB to make a detailed analysis of the dimer and to come to an understanding as to what governs the choice of its curious orientation within the vacancy.