高温高压下体心立方结构和液态铁中自旋纵向涨落的超原胞计算
Longitudinal spin fluctuations in bcc and liquid Fe at high temperature and pressure calculated with a supercell approach
摘要：
由于振动自由度和磁自由度的相互作用，用第一性原理方法研究磁性材料在实际条件下的性质是一项具有挑战性的任务。最困难的贡献，包括在模拟中所代表的纵向磁自由度（LSF），由于其固有的多体性质，尽管如此，计划，使考虑到这种影响的半经典水平已被提出并采用在磁系统的调查。然而，在文献中缺乏振动对LSF的影响的评估。出于这个原因，在这项工作中，我们开发了一个超原胞的约束密度泛函理论的框架内的方法来计算自洽的局部环境依赖的磁矩的大小在顺磁，高温状态下的晶格振动的存在下，在不同的条件下，液态铁。首先，我们考虑的情况下，体心立方铁在居里温度和环境压力。然后，我们进行了类似的分析bcc铁在地球的内核条件下，我们发现，LSF稳定的非零时刻，影响原子力和电子态密度的系统。最后，我们采用目前的计划，在熔点在环境压力下的液态铁，并在地球的外核条件（$p \approx 200$ GPa，$T \approx 6000$ K）。在这两种情况下，我们获得的本地磁矩的大小相媲美的固态同行。
英文摘要：
Investigation of magnetic materials at realistic conditions with first-principles methods is a challenging task due to the interplay of vibrational and magnetic degrees of freedom. The most difficult contribution to include in simulations is represented by the longitudinal magnetic degrees of freedom (LSF) due to their inherent many-body nature; nonetheless, schemes that enable to take into account this effect on a semiclassical level have been proposed and employed in the investigation of magnetic systems. However, assessment of the effect of vibrations on LSF is lacking in the literature. For this reason, in this work we develop a supercell approach within the framework of constrained density functional theory to calculate self-consistently the size of local-environment-dependent magnetic moments in the paramagnetic, high-temperature state in presence of lattice vibrations and for liquid Fe in different conditions. First, we consider the case of bcc Fe at the Curie temperature and ambient pressure. Then, we perform a similar analysis on bcc Fe at Earth's inner core conditions, and we find that LSF stabilize non-zero moments which affect atomic forces and electronic density of states of the system. Finally, we employ the present scheme on liquid Fe at the melting point at ambient pressure, and at Earth's outer core conditions ($p \approx 200$ GPa, $T \approx 6000$ K). In both cases, we obtain local magnetic moments of sizes comparable to the solid-state counterparts.
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