Density Functional Theory of Noncollinear Magnetic Systems

非共线磁系统的密度泛函理论

• 批准号: 0073546
• 负责人: Leonard Kleinman
• 金额: $ 37.2万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-06-01 至 2004-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0073546&HistoricalAwards=false
• 关键词: Density; Functional; Theory; Noncollinear; Magnetic

This award supports theoretical and computational research on a variety of topics relating to the electronic structure of magnetic materials. Neutron scattering cannot distinguish between a spiral spin density wave (SSDW) and ordinary transverse spin density wave's (SDW) polarized in different directions in different domains. It is relatively easy to calculate noncommensurate SSDW's but not SDW's. This research will attempt to verify the widely held belief that Cr has a SDW ground state by calculating the energy versus wave vector SSDW curves and comparing the energies of the commensurate SSDW and SDW ground states. The SSDW ground state of rare earth europium will also be calculated.Also, full potential frozen spin wave calculations will be done for Fe and Ni. A larger spin stiffness correction is expected to be required to obtain magnon dispersion curves in agreement with experiment in the case of Fe because its spins are more itinerant than those of Ni. Also to be calculated are the magnon dispersion curves of rare earth gadolinium. Calculations indicate FeRh is an itinerant antiferromagnet. Although the frozen spin wave scheme will work for antiferromagnets in principle, it is not obvious that it will work in practice. Assuming that FeRh is not found to have a SSDW ground state, the scheme will be tested for calculating magnon dispersion curves on it.The spin stiffness used is a somewhat ad hoc gradient term added to the LSDA (local spin density approximation), but the LSDA as currently applied to SSDW's is stretched beyond its range of validity. Furthermore, the spin stiffness correction contains an arbitrary multiplicative parameter. Ideas will be pursued for obtaining further improvements in density functional approximations fo rnoncollinear magnetic systems. If successful, some of the calculations made for the spin stiffness density functional will be repeated. Other calculations will be done. For example, and in agreement with experiment, the GGA (generalized gradient approximation) yields a magnetic surface for V(001) whereas the LSDA does not. One experiment finds that a monlayer of V on Ag(001) has no net magnetization whereas another finds it to be ferromagnetic. An LSDA calculation finds an antiferromagnetic ground state. GGA calculations will be performed in the belief that they will result in the ferromagnetic state lying below the antiferromagnetic one, and inspire additional experimental work.%%%This award supports theoretical and computational research on a variety of topics relating to the electronic structure of magnetic materials. Calculations will be done using density functional theory to determine the magnetic properties of a variety of materials. These calculations will be compared with experiment and will assist in resolving issues relating to these important magnetic materials***.

该奖项支持与磁性材料的电子结构有关的各种主题的理论和计算研究。中子散射不能区分螺旋自旋密度波（SSDW）和普通横向自旋密度波（SDW）在不同区域中不同方向的极化。不相称的SDW相对容易计算，但SDW不容易计算。本研究将试图通过计算能量与波矢量的SSDW曲线，并比较相应的SSDW和SDW基态的能量，来验证人们普遍认为的Cr具有SDW基态。计算了稀土铕的SSDW基态。同时，将对Fe和Ni进行全势冻结自旋波计算。由于Fe的自旋比Ni的更不稳定，因此需要更大的自旋刚度修正才能得到与实验相符的磁振子色散曲线。还计算了稀土钆的磁振子色散曲线。计算表明FeRh是一种流动的反铁磁体。虽然冻结自旋波方案原则上适用于反铁磁体，但在实践中是否可行尚不明显。假设没有发现FeRh具有SSDW基态，将对该方案进行测试，以计算其上的磁振子色散曲线。使用的自旋刚度是在LSDA（局部自旋密度近似）中添加的一个特别的梯度项，但是目前应用于SSDW的LSDA超出了其有效范围。此外，自旋刚度修正包含一个任意的乘法参数。我们将寻求进一步改进非共线磁系统的密度泛函近似。如果成功，将重复对自旋刚度密度泛函所做的一些计算。其他的计算将会完成。例如，与实验一致，GGA（广义梯度近似）产生V（001）的磁表面，而LSDA则没有。一个实验发现Ag（001）上的V单层没有净磁化，而另一个实验发现它是铁磁性的。LSDA计算发现了一个反铁磁基态。在进行GGA计算时，人们相信它们将导致铁磁态位于反铁磁态之下，并激发额外的实验工作。该奖项支持与磁性材料的电子结构有关的各种主题的理论和计算研究。计算将使用密度泛函理论来确定各种材料的磁性。这些计算将与实验进行比较，并将有助于解决与这些重要磁性材料有关的问题。