Small concentrations of impurities can dramatically change mechanical properties of metals and alloys since they modify bonding and cohesion at grain boundaries. In particular, impurities like B, C, P and S have received considerable attention for their effect on the mechanical properties of Fe. It is known that B and C behave as cohesive enhancers, whereas P and S tend to embrittle iron. Ab initio electronic structure calculations for supercell models of Fe crystals with B, C, P and S impurities have been performed to understand how these impurities modify the electronic states on surrounding atoms The calculations give the charge density distribution, localized densities of states (LDOS) and the total energy of the system. The angular momentum resolved LDOS, when multiplied by slowly varying matrix elements, can be directly related to the experimentally measured electron energy loss near edge structure.

The calculations have been performed using two different methods. One is the Linearized Augmented Plane Wave (LAPW) method, in which the Kohn-Sham equations of density functional theory are self-consistently solved within the Local Density Approximation (LDA) to obtain energies and charge distributions of a crystalline system.