论文标题
耦合自旋1/2纳米仪中分子间交换的理论
Theory of intermolecular exchange in coupled spin-1/2 nanographenes
论文作者
论文摘要
开放式纳米仪可以共价结合，仍然保留其当地时刻，形成相互作用的旋转晶格。以苯纳米摄影师为例，Ovchinnikov-Lieb规则预测了上部结构的基态的旋转，从而预见了分子间交换的迹象。在这里，我们解决了这种系统中分子间交换的基本微观机制。我们发现，通常，三种不同的机制有助于。首先，Hund的铁磁交换促进了重叠轨道中电子的铁磁相互作用。其次，由分子间杂交驱动的超级换档，与安德森动力学交换相同，这是哈伯德 - $ u $ u $能量量表的降低功能，并且始终是抗铁磁磁性。第三，库仑驱动的超级换档，它随着$ u $的函数而增加，并且涉及在整个结构上扩展的激发分子轨道的虚拟激发。我们发现，库仑驱动的superexchange可以是铁磁性或反铁磁性，这是Ovchinnikov-lieb规则。我们使用Hubbard和Extended Hubbard模型的多种配置方法来计算耦合$ s = 1/2 $ s = 1/2 $ s = 1/2 $ s = 1/2 $的交换能，从而解决了远程库仑相互作用对交换相互作用的影响。
Open-shell nanographenes can be covalently bonded and still preserve their local moments, forming interacting spins lattices. In the case of benzenoid nanographenes, the Ovchinnikov-Lieb rules anticipate the spin of the ground state of the superstructure, and thereby the sign of the intermolecular exchange. Here we address the underlying microscopic mechanisms for intermolecular exchange in this type of system. We find that, in general, three different mechanisms contribute. First, Hund's ferromagnetic exchange that promotes ferromagnetic interactions of electrons in overlapping orbitals. Second, superexchange driven by intermolecular hybridization, identical to Anderson kinetic exchange, which is a decreasing function of the Hubbard-$U$ energy scale, and is always antiferromagnetic. Third, a Coulomb-driven superexchange, that increases as a function of $U$, and involves virtual excitation of excited molecular orbitals that are extended over the entire structure. We find that Coulomb-driven superexchange can be either ferro or antiferromagnetic, accounting for Ovchinnikov-Lieb rules. We compute these exchange energies for the case of coupled $S=1/2$ phenalenyl triangulenes, using multi-configurational methods both with Hubbard and extended Hubbard models, thereby addressing the influence of long-range Coulomb interactions on the exchange interactions.
