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Ordering Energy of B2 Alloys Calculated in the Frozen Potential and Harris Approximations

  • W. A. Shelton (a1), D. M. Nicholson (a1), G. M. Stocks (a1), F. J. Pinski (a2), D. D. Johnson (a3), P. Sterne (a4) and W. M. Temmerman (a5)...

Abstract

It has been established that the coherent potential approximation can successfully describe the energy of random alloys [1]. It has also served as the basis of generalized perturbation method [2] and concentration wave [3] xscalculations of the energy of short range ordered alloys. The multisublattice coherent potential, (MCPA) is the natural extension of the CPA with which to address long range order (LRO). Using the recently developed multisublattice coherent potential approximation Korringa Kohn Rostoker [4], (MCPA-KKR) code the elgenvalue sum can be calculated as a function of LRO. This allows the evaluation of the ordering energy by either of two approximations. The frozen potential approximation (FPA) [5] assumes that the muffintin single site potentials do not change as the long range order is varied; the Harris Approximation, (HA) [6], as applied in this work, assumes that the single site charge densities do not change as the long range order is changed. These two methods of calculating the ordering energy will be compared with each other and to experiment for several systems including CuZn, NiAl, and NiAl with zinc additions.

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1. Johnson, D. D., Nicholson, D. M., Pinski, F. J., Gyorffy, B. L., and Stocks, G. M., Phys. Rev. B41, 9701, (1990).
2. Turchi, P.E.A., Stocks, G. M., Butler, W. H., Nicholson, D. M., and Gonis, A., Phys. Rev. B37, 5982, (1988).
3. Gyorffy, B. L., Johnson, D. D., Pinski, F. J., Nicholson, D. M., and Stocks, G. M., The electronic structure and the state of compositional order in metallic alloys. In Stocks, G. M. and Gonis, A., editors, Alloy Phase Stability, volume 163, pages 421-468, Dordrecht (NL), 1989. NATO ASI Series E, Kluwer Academic Publishers. B. L. Gyorffy, and G. M. Stocks, Phys. Rev. Lett., (50):374, (1983).
4. Shelton, W. A., Thesis University of Cincinnati, 1990 (unpublished).
5. Harris, J., Phys. Rev. B31, 1770 (1985); W.M.C. Foulkes and R. Haydock, Phys. Rev. B39, 12520, (1989).
6. Pettifor, D. G., Comm. on Phys. 1, 141 (1976); J. Chem. Phys. 69, 2930, (1978).
7. Andersen, O. K., Rev. B12, 3060, (1975).
8. Averill, F. W., Painter, G. S., Phys. Rev. B41, 10344, (1990).
9. Janak, J. F., Phys. Rev. B9, 3985, (1974).
10. Of course in ASA calculations the spheres can be chosen neutral in which case the FPA is valid through first order in P2-Pf.
11. Sluiter, M., Turchi, P.E.A., Johnson, D. D., Pinski, F. J., Nicholson, D. M., Stocks, G. M., proc. 1987 MRS Fall Meeting, ed. Shapiro, S. M., Moss, S. C., Jorgensen, J. D., vol. 166 (1990).
12. Moruzzi, V. L., private communication.
13. , Rheinhart, Thesis ETH, Zurich, Switzerland (1989), (unpublished).
14. Pinski, F. J., private communication.

Ordering Energy of B2 Alloys Calculated in the Frozen Potential and Harris Approximations

  • W. A. Shelton (a1), D. M. Nicholson (a1), G. M. Stocks (a1), F. J. Pinski (a2), D. D. Johnson (a3), P. Sterne (a4) and W. M. Temmerman (a5)...

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