New band-structure calculations of point-slit angular correlation curves for positron annihilation in Cu single crystals are compared with measurements by Mader and Berko et al. Corrections are applied for the geometrical resolution and for enhancement due to e -e and e -e correlations. A new energy-dependent form of "Kahana enhancement" is proposed that gives excellent agreement between theory and experiment if the core contribution is reduced by a factor of 5. The results qualitatively confirm the enhancement of umklapp contributions derived by Hede and Carbotte. No indication is found for a de-enhancement of the umklapp components proposed by Fujiwara et al. Calculated curves for a-Cuo, Zno, obtained on the basis of a rigid-band model are given for future reference,

An interpretation of the two-dimensional angular correlation of positron annihilation radiation (2D-ACAR) for paramagnetic chromium (Cr) and molybdenum (Mo) is presented. Rather than explaining the significant differences in the resulting k-space occupancies in terms of different Fermi surface (FS) topologies, the recovery of a FS topology for paramagnetic Cr in agreement with band theory (and similar to the Mo experiment) through the application of a recently introduced maximum-entropy-based filtering technique suggests an explanation related to positron wavefunction perturbations.

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The authors present a theoretical and experimental study of the Fermi surfaces (FSs) of Li and the disordered alloys Li1-xMgx (0.6>or=x>0.0) in the BCC phase. Theoretical calculations employ the first-principles fully charge-self-consistent Korringa-Kohn-Rostoker coherent-potential-approximation scheme within the local-density approximation. The experiments involve the two-dimensional angular correlation of positron annihilation radiation measurements on four Li1-xMgx single-crystal specimens with x=0.0, 0.28, 0.40 and 0.60. Good overall agreement is found between experiment and theory with regard to the size and shape of the FS as x is increased from 0.0 to 0.6, although some discrepancies are noted. The question of the critical Mg concentration x=xc at which the FS first makes contact with the Brillouin zone boundary in Li1-xMgx alloys is considered in some detail.

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