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，以促进新磁性材料的设计，特别是单分子磁体（SMMs）和显示磁电耦合的分子多铁性材料（MFs）。在smm中，未配对的电子排列它们的磁矩（它们的自旋）形成磁铁。smm的主要优点是其磁性中心密度高，其性质可以通过化学环境来调节。这使得它们可以应用于新型数据存储材料中，与现有材料相比，其信息密度高达10,000倍。此外，smm可以表现出量子行为，允许它们用作量子比特，量子计算机的构建块。MFs是具有多种铁性质的材料，即可以通过外部影响切换的内部性质，例如可通过电场切换的极化或可通过磁场切换的磁化。在具有磁电耦合（MEC）的mf中，磁场也可以改变磁性（反之亦然）。磁性质的电开关是非常可取的，因为产生强的、快速变化的或空间局域化的电场比产生磁场容易得多。这为传感、数据处理和存储等新型、更小、更节能的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，目前仍需要改进才能成为应用准备：smm遭受不必要的相互作用，因此它们的磁化只能在很短的时间和非常低的温度下保持稳定。MFs需要更强的MEC来实现快速高效的切换。研究人员使用称为自旋哈密顿量的理论模型来描述自旋相互作用。我们提出了一种使用量子化学计算来参数化这些模型的新方法。在具有多个未配对电子的系统的量子化学计算中，考虑到发生的许多不同的电子构型是具有挑战性的。我们的创新之处是运用了主持人安娜·克里洛夫教授开发的自旋翻转方法。自旋翻转计算使用所谓的高自旋态作为起点，其中所有未成对的电子自旋排列，从而形成单一构型。从那里，其他重要的构型是通过翻转单个自旋得到的。通过从第一原理计算自旋哈密顿量，我们不仅可以在合成候选材料之前预测其性质，还可以确定优化自旋相互作用以获得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.