Elastic, thermal and structural properties of platinum Original Research Article

The thermal equation of state (EOS) for platinum has been calculated to 300 GPa and 3000 K using ab initio molecular dynamics employing the local density approximation (LDA) and the projector augmented-wave methods (PAW). Direct ab initio 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 BT0=290.8 GPa and a pressure derivative of BT′=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, α0, temperature derivative of the isothermal bulk modulus, (∂BT/∂T)V, and second temperature derivative of the pressure, (∂2P/∂T2)V, were 1.94×10−5 K−1, −0.0038 GPa K−1, and 1.7×10−7 GPa2 K−2, respectively. A fit to the Mie–Grüneisen–Debye EOS yielded values for the Grüneisen parameter, γ0, and its volume dependence parameter, q, 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.