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In recent years, there has been increasing interest in the specific heat C of insulators and semiconductors because of the availability of samples with different isotopic masses and the possibility of performing ab initio calculations of its temperature dependence C(T ) using as a starting point the electronic band structure. Most of the crystals investigated are elemental (e.g., germanium) or binary (e.g., gallium nitride) semiconductors. The initial electronic calculations were performed in the local density approximation and did not include spin-orbit interaction. Agreement between experimental and calculated results was usually found to be good, except for crystals containing heavy atoms (e.g., PbS) for which discrepancies of the order of 20% existed at the low temperature maximum found for C/T 3 . It has been conjectured that this discrepancies result from the neglect of spin-orbit interaction which is large for heavy atoms (∆0 ∼1.3eV for the p valence electrons of atomic lead). Here we discuss measurements and ab initio calculations of C(T ) for crystalline bismuth (∆0 ∼1.7 eV), strictly speaking a semimetal but in the temperature region accessible to us (T > 2K) acting as a semiconductor. We extend experimental data available in the literature and notice that the ab initio calculations without spin-orbit interaction exhibit a maximum at ∼8K, about 20% lower than the measured one. Inclusion of spin-orbit interaction decreases the discrepancy markedly: The maximum of C(T ) is now only 7% larger than the measured one. Exact agreement is obtained if the spin-orbit hamiltonian is reduced by a factor of ∼0.8.

International audienceAn annealing-driven transition from a chemically disordered A1-like structure to a chemically ordered L10-like phase has been revealed for size-selected CoPt clusters with diameters from 2 to 4 nm, from experiment to theory confrontation. For chemically ordered particles, atypical lattice-parameter ratios c/a are inferred. This ratio is found to be remarkably different depending on the approach used (c/a>1 from x-ray absorption at the Co K edge and c/a≃0.94 from the Pt dominated x-ray diffraction). A first-principles theoretical study accurately explains this astonishing feature and provides a detailed understanding of the element-specific local relaxations, which are crucial in these nanoalloys

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