A potential function for aluminium is derived from phonon dispersion curves. The contribution from short-range multi-ion interactions is substracted from the phonon data, and this affecto markedly the short-range characteristics of the potential. The potential function is used for tho calculation of the energies of intrinsic and extrinsic stacking faults. Certain multi-ion contributions to these energies are also evaluated. The calculation cannot explain the experimentally observed difference between Vntr and yextr, which is attributed here to the interpretation of loop annealing observations in such faults. A re-interpretation gives approximntely 120 mJ/m2 for
Iritroiluc tioriOur knowledge of atomic interactions has increased greatly during the last twenty years. The pair potential approach or its equivalent, the second-order pseudopotential approach, appear to be appropriate only for simple metals, and are in suspect in the case of noble or transition metals. Of the technically important metals, only a hmininni belongs to the first group, but even its treatment suffers from limitations. The selection of the pseudopotential and the screening function is not unique, and for this reason a variety of more or less fundamental pair potentials have been constructed for this metal. I n addition, those third-and higher-order terms in electron-ion interaction which contribute to pairwise atomic interaction are generally omitted from the calculations. Neither has empirical derivation yielded reliable pair potentials, for these are frequently of short range and are fitted to experiniental data by assuming the non-pairwise higher-order terms to be negligible. The pseudopotential theory indicates that the former is a poor assumption, and there is both theoretical and experimental evidence that the latter is not strictly correct in the case of Al.The objective here is t o construct a pair potential for A1 by fitting a long-range function derived from pseudopotential theory to experimental phonon frequencies.It is known that phonon dispersion curves in aluminium are not in agreement with the central force model. This is an indication of non-pairwise multi-ion forces. A large l) Oulu, Finland.
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