Tilt Boundaries In BCC Metals:Comparison of Results Using Different Interatomic Interactions
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TILT BOUNDARIES IN BCC METAIS: COMPARISON OF RESULTS USING DIFFERENT INTERATOMIC INTERACTIONS S. M. FOILES, M. S. DAW AND R. B. PHILLIPS Theoretical Division, Sandia National Laboratories, Livermore, CA 94551-0969 ABSTRACT Two classes of interatomic interactions, the embedded atom method and the model generalized pseudopotential theory are used to calculate the structure of tilt boundaries in bcc metals. These interactions differ in the inclusion of explicitly angular dependent interactions. The results show that these different models of the interactions can lead to qualitatively different predictions for the atomic structure of the boundary. The applicability of the embedded atom method to bcc transition metals is also discussed. INTRODUCTION In this paper, the structure of the symmetric 15(310) tilt boundary in bcc metals will be computed using different representations of the interatomic interactions and the results will be compared. The interactions used will be of two qualitatively different types. First, interactions of the embedded atom method[I] (EAM) type will be used. (The EAM is very similar to the Finnis-Sinclar form[2] of the interactions which have been used previously in bcc metals.) The other type of interactions are the multi-ion interactions developed recently by Moriarty based on the generalized pseudopotential theory[3]. The motivation for this work is two-fold. First the structural calculations will be useful for understanding high resolution images of this boundary. On a more fundamental level, the two classes of interactions differ by the inclusion of explicitly angular dependent interactions. A comparison of the results obtained by the two methods will then give insight into whether the inclusion of such interactions has a significant effect on the atomic structures predicted for defects in general and grain boundaries in particular. The paper is organized as follows. First, the EAM interactions are described including a discussion of the applicability of this form of interatomic interactions to bcc metals. Next, the model generalized pseudopotential theory (MGPT) interactions due to Moriarty will be briefly described and compared to the EAM interactions. Finally, the structures computed for the Z5(310) tilt grain boundary using the two different interactions will be compared for potentials developed for V, Nb and Mo. EAM INTERACTIONS IN BCC METALS The EAM is a semiempirical prescription for modeling the interatomic interactions in metals which was proposed by Daw and Baskes[l]. It has been used successfully for a variety of problems involving fcc transition metals[4]. It has also found limited application to bcc metals. EAM
interactions for bcc metals have been developed by various authors[5, 6, 7] though these interac-
tions have not been as thoroughly tested as in the case of the fcc metals. In addition, the FinnisSinclair form of the interatomic interactions is in practice very similar to the EAM and has been applied to various defect properties in bcc metals[2,8]. In the EAM the tota
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