Dominant density parameters and local pseudopotentials for simple metals

The properties of the simple metals are controlled largely by three density parameters: the equilibrium average valence electron density 3/4πrs3, the valence z, and the density on the surface of the Wigner-Seitz cell, represented here by the equilibrium number Nint of valence electrons in the interstitial region. To demonstrate this fact, and as a refinement of the ‘‘stabilized jellium’’ or ‘‘structureless pseudopotential’’ model, we propose a structured local electron-ion pseudopotential w(r) which depends upon either rs and z (‘‘universal’’ choice for Nint), or rs, z, and Nint for each metal (‘‘individual’’ potential). Calculated binding energies, bulk moduli, and pressure derivatives of bulk moduli, evaluated in second-order perturbation theory, are in good agreement with experiment for 16 simple metals, and the bulk moduli are somewhat better than those calculated from first-principles nonlocal norm-conserving pseudopotentials. Structural energy differences agree with those from a nonlocal pseudopotential calculation for Na, Mg, and Al, but not for Ca and Sr. Our local pseudopotential w(r) is analytic for all r, and displays an exponential decay of the core repulsion as r→∞. The decay length agrees with that of the highest atomic core orbital of s or p symmetry, corroborating the physical picture behind this ‘‘evanescent core’’ form. The Fourier transform or form factor w(Q) is also analytic, and decays rapidly as Q→∞; its first and only zero Q0 is close to conventional or empirical values. In comparison with nonlocal pseudopotentials, local ones have the advantages of computational simplicity, physical transparency, and suitability for tests of density functional approximations against more-exact many-body method

Formation of solid splats during thermal spray deposition

International audienceThis paper reviews the findings of recent research on the formation of solid splats by the impact of thermal spray particles on solid substrates. It discusses methods of describing the substrate, by characterizing both chemical (oxide layers) and physical (surface topography, adsorbed and condensed contaminants) aspects. Recent experiments done to observe impact of thermal spray particle are surveyed and techniques used to photograph particle impact and measure cooling rates described. The use of numerical modeling to simulate impact and deformation of impacting particles is appraised. Two different break-up mechanisms are identified: solidification around the edges of splats; and perforations in the interior of thin liquid films created by droplet spreading without solidification. These two modes can be reproduced in numerical models by varying the value of thermal contact resistance between the splat and substrate. A simple criterion to predict the final splat shape is presented