Describing the spin-polarized transport in molecular junctions by ab-initio calculations

应用从头算密度泛函理论，我们将研究金属铅之间简单有机分子的结构性质。结合密度泛函理论和非平衡态格林函数方法，我们将研究这些系统中与自旋相关的输运性质。我们选择的分子体系将是带有顺磁性过渡金属中心的金属-苯多链夹心化合物Xn(C6H6)m，X=V，Nb，Ta，以及它们的官能化衍生物，附着在铜(111)引线上。这些分子中的过渡金属离子X产生磁矩，通过分子的自旋相关电导将作为这些磁矩(铁磁、反铁磁、非共线)的有序性以及这些磁矩相对于分子的相对取向的函数来研究，由于自旋-轨道相互作用的影响而导致弹道反常磁阻。铁磁性CoCu(111)引线被认为是自旋注入器。除了通常的密度泛函理论方法外，还将研究分子的电荷随吸收细节和外加偏置的变化，包括自相互作用修正的影响。为了实现这些目标，从头算方法在不同的方向上得到了发展，包括对附着在半无限表面上的一维分子结构的全电子输运方案的实施，以及适用于自相互作用修正的方案。

Applying ab initio density functional theory we will study structural properties of simple organic molecules between metallic leads. Combining density functional theory with the nonequilibrium Green function approach we will investigate the spin-dependent transport properties in these systems. Our molecular system of choice will be the metal-benzene multipledecker sandwiches Xn(C6H6)m with paramagnetic transition-metal centers, X=V,Nb,Ta, as well as their functionalized derivatives, attached to Cu(111) leads. The transition-metal ion X in these molecules induces a magnetic moment and the spin-dependent conductance through the molecules will be studied as function of the ordering of these moments (ferromagnetic, antiferromagnetic, noncollinear), and of relative orientation of these moments with respect to the molecule leading to a ballistic anomalous magnetoresistance due to the effect of the spin-orbit interaction. Ferromagnetic CoCu(111) leads are explored as spin-injectors. Charging of the molecules as a function of the details of the absorption and the applied bias will be investigated including effects of the self-interaction correction beyond usual density functional theory methods.To achieve these goal the ab initio methods are developed in various directions including the implementation of an all-electron transport scheme for one-dimensional molecular structures attached to semi-infinite surfaces and a suitable scheme for the self-interaction correction.