We have studied a promising lithium-ion conductor, garnet-type cubic Li oxides, at various Li concentrations. The ab initio calculations performed on these materials revealed two distinct mechanisms of Li-ion transport, with very different energy barriers and a strong dependence on Li distribution. Our findings explain the origin of the vastly varying ionic conductivities at different Li concentrations and suggest possible principles to improve such materials for solid-state electrolyte applications.

Using electronic structure calculations, we demonstrate a global valence alternation in the amorphous ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$, a prototype phase-change alloy for data storage. The resulting $p$ bonding profoundly influences the local atomic structure, leading to right-angle components similar to those in the crystalline counterpart of this chalcogenide glass. The dominance of $p$ bonding is revealed by (i) distributions of the coordination number (CN) and the bond angle, for truly bonded atoms determined based on the electron localization function, and (ii) a direct evaluation of the $p$ (and $s$) orbital occupation probability for the $\mathrm{CN}=3$ Ge atoms that form 90° bonds with neighbors.

A systematic theoretical study is presented for the electronic, mechanical, and optical properties of cubic ${\mathrm{Ti}}_3{\mathrm{N}}_4$ , ${\mathrm{Zr}}_3{\mathrm{N}}_4$ , and ${\mathrm{Hf}}_3{\mathrm{N}}_4$ with the ${\mathit{Th}}_3{P}_4$ structure in the framework of density functional theory. The calculated band structures of ${\mathrm{Ti}}_3{\mathrm{N}}_4$ , ${\mathrm{Zr}}_3{\mathrm{N}}_4$ , and ${\mathrm{Hf}}_3{\mathrm{N}}_4$ show the indirect band gaps of 0.268, 0.909, and $1.00\mathrm{eV}$ , respectively. Furthermore, the optical properties for all three materials were calculated and analyzed in detail. The calculated results are well consistent with available experimental data. Also, it is shown that all these materials have relatively large static dielectric constants at zero frequency, rendering them potential applications in microelectronic devices.

X-ray diffraction and ab initio molecular dynamics simulation studies of molten ${\text{Al}}_{60}{\text{Cu}}_{40}$ have been carried out between 973 and 1323 K. The structures obtained from our simulated atomic models are fully consistent with the experimental results. The local structures of the models analyzed using Honeycutt-Andersen and Voronoi tessellation methods clearly demonstrate that as the temperatures of the liquid is lowered it becomes more ordered. While no one cluster-type dominates the local structure of this liquid, the most prevalent polyhedra in the liquid structure can be described as distorted icosahedra. No obvious correlations between the clusters observed in the liquid and known stable crystalline phases in this system were observed.