第一性原理计算Fe从bcc到hcp结构的相变路径及其磁性边界

本文采用基于密度泛函理论的第一性原理方法,计算了压力作用下Fe从bcc到hcp结构相变的势能面、相变路径以及相变过程中的磁性相边界.结果表明:与Burgers路径不同,相变过程中bcc结构(110)bcc面的剪切和相对滑移相互耦合,并伴随有(110)bcc面间距的减小;这一相变机制可以解释Fe的静高压实验中在相变初期观察到的hcp结构异常.因此,并不需要像Wang和Ingalls提出的那样,在相变过程中引入一个亚稳定的fcc相来解释这些实验结果.对相变势能面的计算表明剪切对相变的发生有激活作用.此外,分析表明相变过程中涉及复杂的磁性转变,相变过渡态位置正好位于磁性相边界上,并对原子磁性对结构转变影响的物理机制进行了讨论.

Ab initio calculations of the pathways and magnetic boundaries for the bcc to hcp transition in Fe

In this work, we calculate the potential energy surfaces, transition paths, and boundaries between various magnetic phases at different pressures for the bcc to hcp structural transition in Fe based on accurate ab initio methods The results indicate that the transition path mainly consists of the coupled shear and shuffle of the (110)bcc planes together with reduction of the (110)bcc interplane distance. This transformation path can explain the anomalous structures of hcp phase observed at the beginning of the transition in the hydrostatic compression experiments. Therefore, a metastable fcc state, which was proposed by Wang and Ingalls, is not needed to account for those observations in the experiments. The calculated potential energy surfaces indicate that the shear is expected to initiate the phase transition. Moreover, there are complex magnetism transitions during the phase transition, and the transition state is almost located at the magnetic phase boundary. In addition, we also discussed the physical origin of the influence of the magnetism on the phase transition.