The site occupation in the Ni-Nb $\mu$ phase is computed from first principles as a function of temperature and composition. It is shown that an empirical rule of thumb based on atomic size, as well as a recently formulated rule based on the approximate point group and the degeneracy of the electronic d-like states, can explain the gross features of the site occupations. However, neither rule explains the distinct behavior of the 12-fold-coordinated $3a$ and $18h$ sites in the $\mu$ phase. The strong Ni preference of the $18h$ site and the mixed occupancy of the $3a$ site is explained on the basis of an analysis of ordering tendencies. Predicted site occupations qualitatively agree with recent Rietveld measurements. A comparison with the compound energy model is made and the limitations of the latter are discussed.

Thermodynamic properties of liquid Al-Cu and Al-Zn alloys are investigated using the free volume model. We also analyse local atomic arrangements and concentration fluctuations in both liquid binary alloys from the determination of the Warren-Cowley short-range order. For liquid Al-Cu alloys, our findings indicate a strong preference for heteroatomic nearest-neighbors bonds on the Cu-rich side and weaker ones in the Al-rich part while for the liquid Al-Zn alloy, a tendency to the phase separation is observed. Basing on Darken’s thermodynamic relationship, diffusivity has been examined for both liquid alloys.

We report results of a comprehensive study of liquid boron with x-ray measurements of the atomic structure and dynamics coupled with ab initio molecular dynamics simulations. There is no evidence of survival into the liquid of the icosahedral arrangements that characterize the crystal structures of boron but many atoms appear to adopt a geometry corresponding to the pentagonal pyramids of the crystalline phases. Despite similarities in the melting behavior of boron and silicon, there is little evidence of a significant structural shift with temperature that might suggest an eventual liquid-liquid phase transition. Relatively poor agreement with the observed damping of the sound excitations is obtained with the simple form of mode-coupling theory that has proved successful with other monatomic liquids, indicating that higher-order correlation functions arising from directional bonding and short-lived local structures are playing a crucial role. The large ratio of the high frequency to the isothermal sound velocity indicates a much stronger viscoelastic stiffening than in other monatomic liquids.