Calphad description at high pressure is a very important topic. Several models have been proposed in the literature. The model proposed by Lu et al. (X.-G. Lu, M. Selleby and B. Sundman, Comput. Coupling Phase Diagr. Thermochem., 29 (2005) 49-55) is very convenient in many aspects. But it has been criticized for giving unphysical extrapolations in certain conditions. We show that this model is indeed suitable if additional constraints on several parameters are made in order to obtain consistent extrapolations when both high pressure and high temperature are considered. This revised model will be applied to the complete description of the Os–Pt system. In this first part, the thermodynamic assessment of platinum in both solid and liquid phases is presented. The use of DFT and phonon calculated data provided in the present work will be shown to be useful for the thermodynamic assessment. A consistent description of Pt at high pressure and temperature (equation of state) including the liquid phase and phase diagram is given for the first time.

高压下的 Calphad 描述是一个非常重要的话题。文献中已经提出了几种模型。Lu等人提出的模型。(X.-G. Lu, M. Selleby 和 B. Sundman, Comput. Coupling Phase Diagr. Thermochem., 29 (2005) 49-55) 在很多方面都非常方便。但它因在某些条件下进行非物理推断而受到批评。我们表明，如果在考虑高压和高温时对几个参数进行额外约束以获得一致的外推，则该模型确实适用。这个修订后的模型将应用于 Os-Pt 系统的完整描述。在第一部分中，介绍了铂在固相和液相中的热力学评估。目前工作中提供的 DFT 和声子计算数据的使用将被证明对热力学评估很有用。首次给出了包括液相和相图在内的 Pt 在高压和高温（状态方程）下的一致描述。