A theory for the Helmholtz free-energy functional Fof inhomogeneous simple liquids is presented in which hard-sphere perturbation theory is utilized to separate F into primarily entropic and internal-energy contributions. The entropy of the hard-sphere reference system is obtained from the weighted-density approximation and the internal energy is determined from an expansion about the uniform-liquid value. The thermodynamic functions of a model Lennard-Jones solid, liquid, and vapor are then calculated and the resulting p-Fphase diagram is found to be in good agreement with all aspects of simulation studies, including the Lindemann parameter along the freezing curve. PACS numbers: 05.70.-a, 64.60.-i, 64.70.Dv
We demonstrate experimentally that a part-per-million addition of Sn solutes in Al-Mg-Si alloys can inhibit natural aging and enhance artificial aging. The mechanism controlling the aging is argued to be vacancy diffusion, with solutes trapping vacancies at low temperature and releasing them at elevated temperature, which is supported by a thermodynamic model and first-principles computations of Sn-vacancy binding. This "diffusion on demand" solves the long-standing problem of detrimental natural aging in Al-Mg-Si alloys, which is of great scientific and industrial importance. Moreover, the mechanism of controlled buffering and release of excess vacancies is generally applicable to modulate diffusion in other metallic systems.
The equilibrium structure and energetics of the crystal-melt interfaces of simple systems are studied using the nonlocal weighted density-functional approximation (%"DA) to the Helmholtz free energy. The WDA, previously used to accurately predict bulk phase coexistence at the melting point, is combined with a new fiexible, two-parameter parametrization of the crystal-melt interfacial region to predict interfacial properties. The parametrization allows for variations in the width of the interface and in the rate of broadening of the sharp density peaks of the crystal through the inter-
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