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In this paper a two-grid algorithm is discussed for the mixed finite element discretization of Poisson's equation. The algorithm is based on a Vanka-type relaxation; the grid transfer operators are selected in accordance with the discretization. Local mode analysis Is used to show that Vanka-type relaxation Is an efficient smoother indeed. By studying the Fourier transform of the error amplification matrix we find that the canonical grid transfer operators are sufficiently accurate for grid independent convergence. However, this conclusion depends on the relaxation pattern used.

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In a previous paper /1/ results were presented for the residual resistivity of 3 4 4d, and s p impurities in Cu obtained by using phase shifts corresponding to a self-consistent alloy potential. Finite cluster model (FCM) results were compared with values obtained from the simple Friedel formula, from the Gupta-Benedek (GB) formula which accounts for bqckscattering, and from the formula by Coleridge, Holzwarth, and Lee, accounting in addition for F e r m i surface effects. It was found that the FCM accounts for backscattering surprisingly well. Since the FCM is the only model available which allows for probing charge transfer and lattice distortion in a rather detailed way, it is attractive to apply this model to that end. In the previous study band effects did not show up as dominant, but only Cu was studied as a host. Therefore i t is interesting t o study also a host with a more complicated F e r m i surface, for which we chose the trivalent Al.In this note we first present and discuss results for 3d impurities in Al.After that charge transfer effects will be shown for some Cu alloys.