Due to their small size and unique properties, single-molecule electronics have long seen research interest from experimentalists and theoreticians alike. From a theoretical standpoint, modeling these systems using electronic structure theory can be difficult due to the importance of electron correlation in the determination of molecular properties, and this electron correlation can be computationally expensive to consider, particularly multiconfigurational correlation energy. In this work, we develop a new approach for the study of single-molecule electronic systems, denoted NEGF-MCPDFT, which combines multiconfiguration pair-density functional theory (MCPDFT) with the non-equilibrium Green’s function formalism (NEGF). The use of MCPDFT with NEGF allows for the efficient inclusion of both static and dynamic electron correlations in the description of the junction’s electronic structure. Complete active space self-consistent field wave functions are used as references in the MCPDFT calculation, and as with any active space method, effort must be made to determine the proper orbital character to include in the active space. We perform conductance and transmission calculations on a series of alkanes (predominantly single-configurational character) and benzyne (multiconfigurational character), exploring the role that active space selection has on the computed results. For the alkane junctions explored (where dynamic electron correlation dominates), the MCPDFT-NEGF results agree well with the DFT-NEGF results. For the benzyne junction (which has a significant static correlation), we see clear differences in the MCPDFT-NEGF and DFT-NEGF results and evidence that NEGF-MCPDFT is capturing additional electron correlation effects beyond those provided by the Perdew–Burke–Ernzerhof functional.

中文翻译：

---

基于多配置对密度泛函理论的分子连接方法

由于它们的小尺寸和独特的特性，单分子电子学长期以来一直受到实验家和理论家的研究兴趣。从理论的角度来看，由于电子相关性在确定分子特性中的重要性，使用电子结构理论对这些系统进行建模可能很困难，而且这种电子相关性在计算上可能很昂贵，尤其是多构型相关能。在这项工作中，我们开发了一种研究单分子电子系统的新方法，称为 NEGF-MCPDFT，它将多配置对密度泛函理论 (MCPDFT) 与非平衡格林函数形式主义 (NEGF) 相结合。MCPDFT 与 NEGF 的使用允许在结的电子结构的描述中有效地包含静态和动态电子相关性。在 MCPDFT 计算中使用完整的活动空间自洽场波函数作为参考，并且与任何活动空间方法一样，必须努力确定包含在活动空间中的适当轨道特征。我们对一系列烷烃（主要是单构型特征）和苯（多构型特征）进行电导和传输计算，探索活性空间选择对计算结果的作用。对于探索的烷烃结（动态电子相关性占主导地位），MCPDFT-NEGF 结果与 DFT-NEGF 结果非常吻合。