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A method for computing electron momentum densities and Compton profiles from ab initio calculations is presented. Reciprocal space is divided into optimally-shaped tetrahedra for interpolation, and the linear tetrahedron method is used to obtain the momentum density and its projections such as Compton profiles. Results are presented and evaluated against experimental data for Be, Cu, Ni, Fe3Pt, and YBa2Cu4O8, demonstrating the accuracy of our method in a wide variety of crystal structures.

We report high-resolution, bulk Compton scattering measurements unveiling the Fermi surface of an optimally doped iron-arsenide superconductor, Ba͑Fe 0.93 Co 0.07 ͒ 2 As 2 . Our measurements are in agreement with first-principles calculations of the electronic structure, revealing both the X-centered electron pockets and the ⌫-centered hole pockets. Moreover, our data are consistent with the strong three dimensionality of one of these sheets that has been predicted by electronic structure calculations at the local-density-approximation-minimum As position. Complementary calculations of the noninteracting susceptibility, 0 ͑q , ͒, suggest that the broad peak that develops due to interband Fermi-surface nesting, and which has motivated several theories of superconductivity in this class of material, survives the measured three dimensionality of the Fermi surface in this family.The discovery of superconductivity in LaO 1−x F x FeAs, a member of the so-called "1111" family of iron-pnictide materials, 1 has triggered intense research into its nature and origin. Tempted by the proximity of the superconductivity in these compounds to an antiferromagnetic spin-density-wave ͑SDW͒ state, many theoretical models have focused on spin fluctuations as the key, 2,3 supported by first-principles calculations of the electronic structure. Such calculations predict four Fermi-surface ͑FS͒ sheets: two hole sheets at the center of the Brillouin zone ͑BZ͒ and two electron sheets centered at its corner. 4,5 In the undoped ͑and lightly doped͒ "1111" compounds the hole and electron sheets are well nested, leading to a broad peak in the noninteracting susceptibility. 2 The spin fluctuations that are thought to develop from this FS instability have already been observed in neutronscattering measurements, 6 and theoretical models suggest that they promote a strong pairing interaction, provided that the order parameter changes phase between the hole and electron FS sheets ͑the so-called s Ϯ model͒. 2,3 Central to such models, however, is a detailed understanding of the topology of the FS; here we present a bulk measurement of the FS of an optimally doped iron-arsenide superconductor, Ba͑Fe 0.93 Co 0.07 ͒ 2 As 2 , alongside complementary calculations of the noninteracting susceptibility, 0 ͑q , ͒. We demonstrate the data are most consistent with a three-dimensional ͑3D͒ FS but that the nesting that is required for the s Ϯ model survives, lending its availability to all iron-pnictide compounds.Ba͑Fe 1−x Co x ͒ 2 As 2 is a member of the "122" family of iron-pnictide superconductors, with a maximum T c ϳ 24 K for x ϳ 0.06. 7,8 Unlike the "1111" family, whose FS is quasitwo-dimensional ͑2D͒, the "122" compounds are predicted by electronic structure calculations to have substantial 3D warping of one of the hole sheets, 5 the degree of which is sensitive to the position of the As with respect to the Fe plane. Experimental studies have not yet adequately resolved whether the electronic structure is better described by the experimental As position or...

The state-dependence of the enhancement of the electron-positron momentum density is investigated for some transition and simple metals (Cr, V, Ag and Al). Quantitative comparison with linearized muffin-tin orbital calculations of the corresponding quantity in the first Brillouin zone is shown to yield a measurement of the enhancement of the s, p and d states, independent of any parameterizations in terms of the unscreened electron density local to the positron. An empirical correction that can be applied to a first-principles state-dependent model is proposed that reproduces the measured state-dependence very well, yielding a general model for the enhancement of the momentum distribution of positron annihilation measurements, including those of angular correlation and coincidence Doppler broadening techniques. arXiv:1005.4909v2 [cond-mat.str-el]