Theoretical Framework for Modeling Field-Dependent Properties of Molecule-Based Magnetic Materials by using Spin-Flips

我们计划开发高精度的计算机模型，以便于设计新的磁性材料，特别是显示磁电耦合的单分子磁体(SMM)和分子多铁体(MFS)。在SMM中，未配对的电子排列它们的磁矩(它们的自旋)以形成磁铁。SMM的主要优点是其高密度的磁中心，并且其性质可以通过化学环境来调节。这使得它们在新型数据存储材料中的应用具有比现有材料高出10000倍的信息密度。此外，SMM还可以表现出量子行为，允许将它们用作量子计算机的构建块量子比特。MF是具有多种铁性的材料，即可以通过外部影响转换的内部属性，如可通过电场切换的偏振或可通过磁场切换的磁化。在具有磁电耦合(MEC)的MFS中，磁性质也可以通过电场来改变(反之亦然)。由于产生强的、快速变化的或空间局域化的电场比产生磁场容易得多，所以磁性质的电切换是非常理想的。这为新的、更小、更节能的传感设备以及数据处理和存储设备开辟了许多应用。SMM和MFS都依赖于对自旋之间相互作用的精确控制，目前这些相互作用仍然需要改进才能应用：SMM受到不必要的相互作用的影响，因此它们的磁化只在很短的时间和非常低的温度下保持稳定。MFS需要更强大的MEC来实现快速高效的切换。研究人员使用称为自旋哈密顿的理论模型来描述自旋相互作用。我们提出了一种利用量子化学计算将这些模型参数化的新方法。在对具有多个未配对电子的系统进行量子化学计算时，考虑到出现的许多不同的电子构型是具有挑战性的。我们的创新是应用了我的东道主安娜·克雷洛夫教授开发的旋转翻转方法。自旋翻转计算使用所谓的高自旋态作为起点，其中所有未配对的电子自旋都排列在一起，从而形成单一组态。通过从第一原理计算自旋哈密顿量，我们不仅可以在合成之前预测候选材料的性质，还可以确定优化自旋相互作用以实现所需功能的设计原则。

We plan to develop high-accuracy computer models to facilitate the design of new magnetic materials, specifically of single-molecule magnets (SMMs) and of molecular multiferroics (MFs) that display magneto-electric coupling. In SMMs unpaired electrons align their magnetic moments (their spins) to form a magnet. Major advantages of SMMs are their high density of magnetic centers and that their properties can be tuned by the chemical environment. This allows their application in novel data storage materials with up to 10000x higher information density compared to current materials. Also, SMMs can exhibit quantum behavior, allowing their use as qubits, the building blocks of quantum computers.MFs are materials with multiple ferroic properties, i.e. internal properties that can be switched by external influence, such as polarization switchable by an electric field or magnetization switchable by a magnetic field. In MFs with magneto-electric coupling (MEC), magnetic properties may also be switched by electric fields (and vice versa). Electric switching of magnetic properties is highly desirable since it is far easier to generate strong, quickly varying or spatially localized electric fields than magnetic ones. This opens up many applications in novel, smaller and more energy-efficient devices for sensing and for data processing and storage.Both SMMs and MFs rely on precise control over the interactions between spins which currently still require improvement to become application-ready: SMMs suffer from unwanted interactions so that their magnetization only remains stable for short times and at very low temperatures. MFs need stronger MEC for fast and efficient switching. Researchers use theoretical models called spin Hamiltonians to describe spin interactions. We propose a new way to parametrize these models using quantum chemical computations.In quantum chemical calculations on systems with multiple unpaired electrons, it is challenging to take into consideration the many different electron configurations that occur. Our innovation is to apply a spin-flip approach developed by my host Prof. Anna Krylov. Spin-flip calculations use so called high-spin states as a starting point, in which all unpaired electron spins are aligned, thereby forming a single configuration. From there, other important configurations are obtained by flipping individual spins.By calculating the spin Hamiltonian from first-principles, we will not only predict properties of candidate materials before they are synthesized but also identify design principles that optimize spin interactions for desired functionality.