A study of the applicability of many-body central force potentials in NiAl and TiAl

The applicability and characteristics of the central force many-body potentials of Finnis-Sinclair-type for NiAl and TiAl are investigated by studying the variation of the energy of these compounds with structural transformations that correspond to three distinct paths: tetragonal (B2 --> L1(0)), trigonal(B2 --> L1(1)) and hexagonal (B2 --> B19). The energy was computed using both the central force potentials and the full potential linearized augmented plane waves (FLAPW) ab initio method. Comparison of these two calculations provides a means for the analysis of the efficacy of the potentials. The central force many-body potentials reproduce the results of ab initio calculations very satisfactorily for NiAl. This propounds that they are sufficient in atomistic modelling of lattice defects in this compound. For TiAl the central force potentials mimic the results of ab initio calculations qualitatively but are unable to differentiate adequately between structures with practically the same separations of the first and second neighbours. However. the present study provides a justification for the use of these potentials when investigating extended defects in which separations of the first and second nearest neighbours differ significantly from those in the L1(0) structure.