铁的相变和热力学性质的第一性原理计算

First-Principles Calculations for Phase Transitionand Thermodynamic Properties of Iron

铁在高温高压下的结构和物理性质对于其在工程技术方面的应用有着非常重要的意义.采用基于密度泛函理论的平面波赝势方法,研究了铁从bcc结构到hcp结构的马氏体相变,并利用准谐德拜模型获得了铁的bcc结构和hcp结构的热力学性质.结果发现:零温下,铁从bcc结构到hcp结构的相变压强为13 GPa,与实验及其他理论符合得很好.通过准谐德拜模型,研究了压强和温度对铁的相对体积V/V0,德拜温度Θ和比热CV的影响.计算结果表明在温度低于1 000 K时,准简谐的德拜模型可以对Fe的热力学性质进行有效描述,而且计算量相对于冻声子近似和从头算分子动力学而言大大降低.

The structure and physical properties of iron at high pressure and high temperature are very important in many applications in the engineering and technology.The authors studied the martensitic phase transition from bcc phase to a hcp phase in Fe based on density-function theory.Employing the plane-wave pseudopotentional method,and the thermodynamic properties of the bcc and hcp structures have been obtained through the quasi-harmonic Debye model.It is found that the zero-temperature transition pressure from bcc to hcp structure is 13 GPa,which is well consistent with the experimental data and other theoretical results.Moreover,the dependences of the relative volume V/V0,the Debye temperature Θ and the specific heat CV on the temperature T and pressure p are also obtained successfully.The results show that the quasi-harmonic Debye model can be used to compute efficiently the thermodynamic properties of Fe below the temperature of 1 000 K,which is much less intensive in the computation than the calculation by the frozen-phonon method and ab initio molecular kinetics.