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We develop ion-ion pair potentials for Al, Na and K for densities and temperatures relevant to the warm-densematter (WDM) regime. Furthermore, we emphasize non-equilibrium states where the ion temperature Ti differs from the electron temperature Te. This work focuses mainly on ultra-fast laser-metal interactions where the energy of the laser is almost exclusively transferred to the electron sub-system over femtosecond time scales. This results in a two-temperature system with Te > Ti and with the ions still at the initial room temperature Ti = Tr. First-principles calculations, such as density functional theory (DFT) or quantum Monte Carlo, are as yet not fully feasible for WDM conditions due to lack of finite-T features, e.g. pseudopotentials, and extensive CPU time requirements. Simpler methods are needed to study these highly complex systems. We propose to use two-temperature pair potentials Uii(r, Ti, Te) constructed from linear-response theory using the non-linear electron density n (r) obtained from finite-T DFT with a single ion immersed in the appropriate electron fluid. We compute equilibrium phonon spectra at Tr which are found to be in very good agreement with experiments. This gives credibility to our non-equilibrium phonon dispersion relations which are important in determining thermophysical properties, stability, energy-relaxation mechanisms and transport coefficients. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) |
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