Elastic, thermal and structural properties of platinum
Résumé
The thermal equation of state (EOS) for platinum has been calculated to 300 GPa and 3000 K using molecular dynamics employing the local density approximation (LDA) and the projector augmented-wave methods (PAW). Direct molecular dynamics avoids the simplifying assumptions inherent in empirical treatments of thermoelasticity. A third-order Birch-Murnaghan equation EOS fitted to the 300 K data yielded an isothermal bulk modulus of = 290.8 GPa and a pressure derivative of = 5.11, which are in better agreement with the measured values than those obtained by previous calculations. The high-temperature data were fitted to a thermal pressure EOS and a Mie-Grüneisen-Debye EOS. The resulting calculated thermal expansion coefficient, α, temperature derivative of the isothermal bulk modulus, (/, and second temperature derivative of the pressure, (/, were 1.94x10 K, -0.0038 GPaK, and 1.7 x10 GPaK, respectively. A fit to the Mie-Grüneisen-Debye EOS yielded values for the Grüneisen parameter, , and its volume dependence parameter, of 2.18 and 1.75, respectively. An analysis of our data revealed a strong volume dependence of the thermal pressure of platinum. We also present a qualitative analysis of the effects of intrinsic anharmonicity from the calculated Grüneisen parameter at high temperatures.
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