CAMD, Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.
J Phys Condens Matter. 2023 Jan 4;35(10). doi: 10.1088/1361-648X/acab4b.
We present a plane wave implementation of the magnetic force theorem, which provides a first principles framework for extracting exchange constants parameterizing a classical Heisenberg model description of magnetic materials. It is shown that the full microscopic exchange tensor may be expressed in terms of the static Kohn-Sham susceptibility tensor and the exchange-correlation magnetic field. This formulation allows one to define arbitrary magnetic sites localized to predefined spatial regions, hence rendering the problem of finding Heisenberg parameters independent of any orbital decomposition of the problem. The susceptibility is calculated in a plane wave basis, which allows for systematic convergence with respect to unoccupied bands and spatial representation. We then apply the method to the well-studied problem of calculating adiabatic spin wave spectra for bulk Fe, Co and Ni, finding good agreement with previous calculations. In particular, we utilize the freedom of defining magnetic sites to show that the calculated Heisenberg parameters are robust towards changes in the definition of magnetic sites. This demonstrates that the magnetic sites can be regarded as well-defined and thus asserts the relevance of the Heisenberg model description despite the itinerant nature of the magnetic state.
我们提出了一种平面波实现的磁力定理，为提取参数化磁性材料经典海森堡模型描述的交换常数提供了一个第一性原理框架。结果表明，完整的微观交换张量可以表示为静态 Kohn-Sham 磁化率张量和交换关联磁场。这种表述允许任意定义局域到预定义空间区域的磁性位，从而使寻找海森堡参数的问题与问题的任何轨道分解无关。磁化率是在平面波基中计算的，这允许对未占据的能带和空间表示进行系统的收敛。然后，我们将该方法应用于研究已久的计算体 Fe、Co 和 Ni 的绝热自旋波谱的问题，发现与以前的计算结果吻合良好。特别是，我们利用定义磁性位的自由度来表明，所计算的海森堡参数对磁性位定义的变化具有鲁棒性。这表明磁性位可以被视为明确的，因此尽管磁性状态是巡游的，但海森堡模型描述仍然是相关的。
