Thermodynamics of copper and nickel: Band-structure effects and their disappearance at high temperatures

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Abstract
The electronic contribution to the equation of state of copper and nickel is calculated from first principles on the basis of density-functional theory. Two methods are used. The first method is the full quantum statistical model, obtained from an extension of the Thomas-Fermi model; it neglects band-structure effects and yields almost the same results for the two metals. The second method is the finite-temperature linear muffin-tin orbitals band-structure method, based on the local-density approximation. This method yields big differences between the behaviors of the two metals at low temperatures in agreement with experiment. At high temperatures the band-structure effects gradually disappear, and the quantum statistical model results are approached.