It has been suggested that icosahedral short-range order (SRO) occurs in deeply undercooled melts of pure metallic elements. We report results of first-principles molecular dynamics simulations for stable and undercooled zirconium liquids. Our results emphasize the occurrence of a local order more complex than the icosahedral one. For stable liquid, the local order is interpreted on the basis of a competition between a polytetrahedral SRO and a bcc-type SRO. We also demonstrate that a bcc-type SRO increases with the degree of undercooling.

The structural and dynamic properties of calcium aluminosilicate (CaO-Al2O3)1-x(SiO2)x melts with low silica content, namely, along the concentration ratio R = 1 are studied by classical molecular dynamics. An empirical potential has been developed here on the basis of our previous ab initio molecular dynamics. The new potential gives a description of the structural as well as the dynamics with a good accuracy. The self-intermediate scattering function and associated α-relaxation times are analyzed within the mode-coupling theory. Our results indicate a decrease of the fragility whose structural origin is a reduction of the number of fivefold coordinated Al atoms and non-bridging oxygen.

X-ray diffraction experiments and ab initio molecular dynamics (AIMD) simulations have been performed to investigate the atomic structure of liquid silicon into the deeply supercooled region. The levitation technique used has made it possible to extend the measurements down to a temperature of 1458 K, 230 K below the equilibrium melting point. The x-ray and AIMD results, which are in reasonable agreement, show conclusively that the tetrahedral order is reinforced and that the coordination number decreases as the liquid is supercooled, with implications for the liquid–liquid phase transition.

We present a study of dynamic properties of liquid aluminum using density-functional theory within the local-density (LDA) and generalized gradient (GGA) approximations. We determine the temperature dependence of the self-diffusion coefficient as well the viscosity using direct methods. Comparisons with experimental data favor the LDA approximation to compute dynamic properties of liquid aluminum. We show that the GGA approximation induce more important backscattering effects due to an enhancement of the icosahedral short range order (ISRO) that impact directly dynamic properties like the self-diffusion coefficient. All these results are then used to test the Stokes-Einstein relation and the universal scaling law relating the diffusion coefficient and the excess entropy of a liquid. Increasing demands to optimize methods and facilities for material processing technologies such as melting, refining, or casting metallic alloys are boosting the precise knowledge of thermophysical properties of these alloys. The main goals are an improvement of the final product quality, an enhancement of the process efficiency, and an economical consumption of resources and energy. More particularly, as the solidification process of a liquid alloy has a strong impact on the structure and properties of the solid material, the understanding of the behavior and more particularly the knowledge of the thermophysical properties of molten alloys prior to solidification are essential for the development of materials with predetermined characteristics. For instance, it is known that properties of lightweight aluminum-based alloys are affected by the temperature conditions of melting and casting 1 , and the knowledge of the diffusion process in their liquid phases is hence a necessity.Among all thermophysical properties, diffusion coefficients are known to play a prominent role for a detailed understanding of the solidification process including crystal growth 2-4 and vitrification 5 . Quite surprisingly, experimental values for liquid aluminum and its alloys are scarce. Their direct measurements in liquid alloys are mostly made using so-called capillary tube methods that require isotopes as tracers. However, the influences of convective flow on the diffusion profile during annealing can be a big problem 6 . As a consequence, self-diffusion coefficients D can be overestimated and published values often differ by a factor of 2. Moreover, radioactive isotopes are not available for aluminum. D are also often obtained indirectly from experimental determinations of the shear viscosity coefficients, g, easier to measure and the use of the Stokes-Einstein (SE) relation 7 , D SE 5 k B T/ 2p Rg, k B being Boltzmann's constant and R is an effective atomic diameter taken as the position of the first peak of the pair-correlation function. If the applicability of the SE relation to liquid metals is well accepted above their melting temperatures, the scatter of experimental viscosity values is important in the case of aluminum 8 , reflecting difficulty of...