Development and application of tight binding and density functional methods for light elements in steels
A coherent transferable tight-binding (TB) parameterization of charge transfer and electronic potentials has yet to be developed for the Fe-C interaction. While interatomic potentials have been obtained for this interaction, recent findings show that the results from these potentials are inconsistent with DFT calculations and do not give an accurate portrayal of chemical bonding in the system.
In this project DFT calculations performed and the bonding interaction of Fe-C is extracted and transferred to a TB construction. The interatomic repulsion is then parameterized to obtain agreement with DFT calculations. This method has been able to produce a correct hierarchy of relevant Fe-C structures, including the interstitial occupancy of carbon in iron. By incorporating a simple parameterization based on physical insights, this method may be used to study of systems containing thousands of atoms using a single desktop computer. Given that a variety of light elements are introduced into steel for mechanical properties enhancement, we will use this procedure to obtain a TB description of additional elements providing the capability to calculate a range of solutes in iron. Additionally, these TB models will be employed for bond order potential (BOP) development for the calculation of even larger systems, bridging the length scales from the electronic to micro-scale atomistic simulations.
Excess enthalpies of carbon in hcp, bcc, and fcc iron.
Bonding parameterization of the Fe-C interaction.
Comparison between DFT and tight-binding of the excess enthalpies of carbon in hcp, fcc, and bcc iron.