Sub-project A1: ab initio Quantum chemistry of the Fe-Mn-C system

Prof. Dr. rer. nat. Dronskowski (Department of Inorganic Chemistry, RWTH Aachen)

A1
A1
Ab initio quantum chemistry investigates structural, electronic and magnetic properties of selected phases of the system Fe‒Mn‒Al‒C. The methods employed comprise Density Functional Theory, molecular dynamics as well as subsequent bonding analysis. For this purpose, the project calculates thermodynamic values such as (free) enthalpies of formation in order to understand the structures on an atomistic scale and detect ordering phenomena that are essentially inaccessible by experiments. In the upcoming period the project focuses on the roles of hydrogen and the κ-phases.

This sub-project will develop spin-conditioned structure models for the different phases, which occur in Mn-rich steels. This contains already known crystalline atomic sub-structures as well as the lattice defects typically occurring in steel. The structure models will be optimized concerning all parameters and afterwards binding-theoretically interpreted. By means of the permanent exchange of results among the different sub-projects, macroscopic measured variables will be chemically interpreted in order to systematically develop the models.

 

TP A1
 TP A1
The atomic binding models are principally based on density functional (pseudo-potentials, PAW, all electronic procedures) methods, however occasionally high-precision shape wave functional based approaches for molecular clips will be used in order to validate the density functional theory. The analysis is based on the calculations of the total energies and on the heats of formation of the single phases (esp. γ-austenites, α’- and ε-martensite) and symbolizes insofar a condition-free single component for the thermodynamic characterization of steel materials. Quantum chemical binding analyses in form of Crystal-Orbital-Hamilton-Populations (COHP) allow conclusions on material properties and an extrapolation on alternative chemical compositions. The extraction of physical quantities like the magnetic properties and mechanic hardness of bulk material against the composition leads to theoretical phase diagrams, which clear the way for improved, so far unknown steels. For the realization of the chemical understanding of the development of typical steel structure characteristics (esp. stacking faults, offsets, twinning, grain boundaries) or transformation processes (exp. γ/α-transformation), molecular dynamic simulations will be carried out.

 

In the long-term, a complete chemical understanding of the chemical-physical properties as function of the electron structure and the chemical binding is strived for under the approximation of the absolute temperature zero-point in sub-project A1. Therefore semi-quantitative predictions concerning unknown systems should be finally possible without detailed calculations of the electron structure.