Spin-Polarized Electron Transport Across Metal-Organic Molecules: A Density Functional Theory Approach
Spin-Polarized Electron Transport Across Metal-Organic Molecules: A Density Functional Theory Approach
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DOI：
10.1021/ct4000263
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发表时间：
2013-06-01
影响因子：
5.5
通讯作者：
Bagrets, Alexei
中科院分区：
文献类型：
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作者：
Bagrets, Alexei
在分子自旋电子学领域，实验技术已经达到了在单分子水平上探索量子电子输运与磁性之间相互作用的可行阶段。一个例子是自旋极化STM，它可以探测通过沉积在磁性表面的有机分子的局部电流。纳米尺度系统的原子复杂性要求对自旋相关输运现象进行第一性原理描述，例如，基于非平衡格林函数（NEGF）形式主义与密度泛函理论（DFT）的融合。然而，对于具有过渡金属电极的分子结，计算潜在的Kohn-Sham哈密顿量可能是一个具有挑战性的问题：需要同时准确地描述自旋有序磁表面以及分子的电子结构。在目前的工作中，我们为这个问题提供了一个解决方案。我们提出了一个标准量子化学包内的NEGF形式的实现，具有自能的有效近似，它既考虑了吸收边界条件，也考虑了铁磁电极中能带的交换分裂。我们展示了一种模拟各种磁性结构的能力，包括纳米级畴壁，这是当具有很少自旋中心的分子与不同磁化的储层接触时实现的。本文讨论了分子尺度上产生的磁阻效应，包括Ni原子尺度的接触、电子在典型分子磁铁（钒苯多层簇）上的传递以及通过co -酞菁的隧穿。此外，我们在DFT+U方法中验证了磁性非平凡解对电子相关性的稳定性。
In the field of molecular spintronics, experimental techniques have achieved a stage where it is feasible to explore the interplay between quantum electron transport and magnetism at the single molecule level. An example is a spin-polarized STM, which can probe local electrical currents through organic molecules deposited on magnetic surfaces. The atomistic complexity of nanoscale systems calls for a first-principles description of spin-dependent transport phenomena, e.g., based on the nonequilibrium Green's function (NEGF) formalism merged with density functional theory (DFT). However, for the case of molecular junctions with transition metal electrodes, a computation of the underlying Kohn-Sham Hamiltonian can be a challenging problem: a simultaneous and accurate description of spin ordered magnetic surfaces together with the electronic structure of a molecule is required. In the present work, we provide a solution for this problem. We present an implementation, within a standard quantum chemistry package, of the NEGF formalism with an efficient approximation for the self energy, which accounts both for absorbing boundary conditions and for exchange splitting of the energy bands in ferromagnetic electrodes. We demonstrate an ability to simulate a variety of magnetic configurations including nanoscale domain walls, which are realized when a molecule with few spin centers is brought in contact with differently magnetized reservoirs. The magnetoresistance effect arising on the molecular scale is discussed based on examples including Ni atomic sized contact, electron transport across a prototypical molecular magnet (vanadium benzene multidecker cluster), and tunneling through Co-phthalocyanine. Furthermore, we verify the stability of magnetically nontrivial solutions against electron correlations within the DFT+U approach.