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A New Method of Evaluating the Explicit Magnetic- State-Dependent Energy in Semi-Empirical Calculations of Iron.
Final rept. Jul 94,
ARMY RESEARCH LAB WATERTOWN MA MATERIALS DIRECTORATE
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The existing semi-empirical methods for use in atomic computer simulations in iron such as various modifications of the Embedded Atom Method have not explicitly taken account of the ferromagnetism per se. Rather, the adjustable parameters just have been fitted to mechanical and thermal properties of iron. However, when the magnetic properties are essential in affecting localized atomic behavior e.g. in the vicinity of crystal defects, these methods may be inadequate. To remedy the situation, a procedure is suggested of explicitly calculating the magnetic contribution to the energy of individual atoms, as a function of their atomic environment. The method uses the Stoner approach, as previously developed in, and a data base obtained by the LMTO-Stoner calculations on BCC Fe under hydrostatic and tetragonal deformations, and Fe free surf aces. The procedure may be incorporated in any semi-empirical method the ferromagnetic contributions to the bulk moduli, C11, C12 and C44 are easily calculated and may be subsequently used in adjusting the semi-empirical Method parameters. Preliminary testing shows a good agreement with the magnetic properties obtained by the LMTO-Stoner calculations.
APPROVED FOR PUBLIC RELEASE