Ab initioelectronic-structure calculations on the Nb/Zr multilayer system

Ab initio electronic-structure calculations are performed for the Nb/Zr metallic multilayer system in the coherent bcc structure and in the incoherent bcc/hcp structure, observed for small and larger modulation wavelengths, respectively. A new calculational scheme, the localized-spherical-wave method, has been used. This method is optimized for handling large unit cells since it avoids laborious lattice summations. For the coherent structure a range of 1 to 6 monolayers for each metal is considered. The results for the incoherent structure are restricted to 5 monolayers per constituent metal. A model for the Nb/Zr incoherent bcc/hcp unit cell is given, including a relaxed structure at the interface, which leads to 55 atoms inside the unit cell. The measured modulation-wavelength dependence of the electronic specific-heat coefficient γ and the superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$ are explained in terms of the calculated results for the density of states. Fur- thermore, the coherent to incoherent structural phase transition is in agreement with the modulation-wavelength dependence of the total energies. The effects of multilayering both on the density of states and the band structure are traced by comparing the results with those for the constituent pure metallic systems.